Sellita SW300-1 Dimensions, Stem Height & Technical Data

The Sellita SW300-1 is an 11½-ligne Swiss automatic mechanical movement used in refined, slim, independent, premium, and modern production watches.

For watch case design, the SW300-1 should not be treated as a simple thin movement with a diameter and height. It is a fixed internal mechanical system with a defined casing envelope, stem-axis relationship, dial-side architecture, rotor clearance requirement, hand-height dependency, date or no-date execution, movement-retention needs, sealing constraints, and service-access requirements.

The headline dimensions identify the movement.

They do not define the finished watch case.

A professional SW300-1 case must resolve four linked engineering groups:

movement location, holder strategy, anti-rotation, and retention
radial clearance, axial clearance, rotor clearance, and caseback stiffness
stem-axis, crown and stem alignment, dial, date, hand-height, rehaut, and crystal relationships
sealing, tolerances, assembly, inspection, prototype validation, and service access

HorologyCAD treats the SW300-1 as a benchmark movement for slim movement-led watch case design because it demonstrates a critical engineering problem:

A thin movement does not automatically create a thin watch.

The SW300-1 gives the designer a lower internal movement height than many standard automatic calibres, but the advantage is preserved only if the surrounding case architecture is resolved efficiently. Rotor space, caseback stiffness, crown alignment, hand clearance, sealing geometry, and tolerance control can easily consume the apparent thickness benefit if they are handled late or casually.

This page separates two information layers:

Official Sellita Manufacturer Data

Specifications, dimensions, movement functions, technical relationships, and casing references defined by Sellita documentation.

HorologyCAD Engineering Interpretation

Case-design guidance explaining how those manufacturer references affect movement location, radial clearance, axial clearance, rotor clearance, crown and stem alignment, hand clearance, sealing, manufacturability, assembly, serviceability, and prototype validation.

Manufacturer documentation defines the movement.

HorologyCAD explains what that movement requires from the case.

SW300-1 Quick Reference

Specification	Manufacturer reference
Calibre	Sellita SW300-1
Movement type	Swiss automatic mechanical
Ligne size	11½ lignes
Overall movement diameter	Verify against exact SW300-1 execution / current technical document
Case-fitting diameter	25.60 mm
Movement height	3.60 mm
Frequency	28,800 A/h / 4 Hz
Jewels	25
Running time	42 hours in older technical documentation; later/current executions may be listed around 56 hours
Winding	Automatic and manual
Stop seconds	Yes
Display	Central hours, minutes, and seconds; date or no-date depending on execution
Date correction	Quick correction in documented date executions
Oscillating weight	Central rotor with ball-bearing support
Balance lift angle	51°
Standard design role	Slim Swiss automatic movement
Case-design status	Execution dependent

Ligne Size Note

The ligne is a traditional Swiss and French watchmaking unit used to classify movement size. One ligne equals 2.2558 mm, although ligne classifications are nominal and should not be treated as controlling engineering dimensions.

For watch-case design and CAD development, use the movement’s official metric dimensions rather than the ligne classification.

SW300-1 Quick Reference Card

The 25.60 mm case-fitting diameter and 3.60 mm movement height are important manufacturer references.

They are not a finished case design.

The 25.60 mm dimension identifies the principal manufacturer-defined casing-fit reference.

The 3.60 mm movement height identifies the movement height, not the final watch thickness.

Final case geometry must additionally account for:

locating surfaces
holder or casing-ring geometry
assembly clearance
anti-rotation control
movement-retention features
dial support
dial thickness
selected hand height
hand-to-crystal clearance
rotor clearance
caseback internal depth
caseback stiffness
crown and stem alignment
crown-tube support
gasket systems
crystal retention
manufacturing variation
finishing allowance
service access

A movement dimension becomes useful only when its function within the complete watch system is understood.

SW300-1 Quick Reference Card

Official Manufacturer Source

Item	Reference
Manufacturer	Sellita Watch Co. SA
Calibre	SW300-1
Primary document	Sellita SW300 / SW300-1 Technical Documentation
Current HorologyCAD source status	Manufacturer documentation identified and checked
HorologyCAD archive reference	HC-MTS-SW300-1

The official Sellita technical document is the primary source for manufacturer-defined information on this page.

It contains information relating to:

movement specifications
winding and testing
timing and performance criteria
component identification
movement assembly
automatic winding assembly
casing components
casing clamps
dial fastening
calendar display
setting-stem positions
oscillating weight
fine regulation
movement diameter
case-fitting diameter
movement height
frequency
running time
jewel count
balance lift angle

Where information is described as official manufacturer data, it should be traceable to the relevant Sellita document section.

The technical document does not remove the need to inspect the exact movement and components used in the project.

Manufacturer-Document Use

The original Sellita technical documentation should be linked for attribution and verification.

The manufacturer drawings contain protected technical material. HorologyCAD should therefore not reproduce complete Sellita drawings without the appropriate permission.

HorologyCAD technical visuals and explanations should be:

independently created
clearly source-attributed
based on verified manufacturer references
explanatory rather than copied
labelled according to source status

This maintains a clear distinction between:

Sellita documentation
HorologyCAD engineering interpretation
HorologyCAD original explanatory material

Readers should consult the original manufacturer document for the complete Sellita specification.

Verification and Revision Notes

Item	Status
Manufacturer	Sellita Watch Co. SA
Calibre	SW300-1
Primary source	Sellita SW300 / SW300-1 Technical Documentation
Initial HorologyCAD source review	22 June 2026
Manufacturer documentation audit	Completed against identified available technical documentation
Physical movement validation	Pending
Prototype validation	Pending
Page status	Manufacturer-documentation audited flagship draft

Verification Scope

The manufacturer specifications and principal case-integration relationships used on this page have been checked against identified Sellita SW300 / SW300-1 technical documentation.

The audit covers:

headline specifications
case-fitting diameter
movement height
frequency
jewel count
running time in the identified document
balance lift angle
basic movement functions
date-window execution
setting-stem positions
oscillating-weight description
stop-seconds function
fine timing device
winding-test information
movement-grade context
casing-clamp and component references where identifiable

HorologyCAD guidance concerning finished cavity sizing, holder strategy, radial clearance, axial clearance, anti-rotation, caseback architecture, rotor protection, sealing, tolerances, assembly, inspection, slim-case stiffness, and prototype acceptance is engineering interpretation.

It is not a universal set of Sellita-prescribed case dimensions.

Configuration Warning

Final case geometry must be checked against:

physical calibre marking
exact SW300-1 execution
current technical document
date or no-date configuration
selected hand-fitting height
dial construction
setting-stem option
casing-clamp or holder arrangement
crown and tube system
actual movement sample where practical

Nominal similarity to the ETA 2892-A2, Sellita SW200-1, ETA 2824-2, or another 11½-ligne Swiss automatic movement does not prove complete casing interchangeability.

Power-Reserve Warning

Older SW300-1 technical references identify a 42-hour running time.

Later or current SW300-family executions may be encountered with longer quoted running times, including around 56 hours depending on execution and supplier documentation.

Power reserve should therefore be treated as execution- and document-dependent.

For case design, this distinction usually affects specification, procurement, product positioning, and movement identification more than the basic movement-to-case envelope.

The exact movement execution should still be recorded before CAD release.

SW300-1 Compared With Other Common Watch Movements

The SW300-1 is one of several common automatic movements used in modern watch case design.

Comparing it with alternatives such as the Sellita SW200-1, ETA 2824-2, ETA 2892-A2, Miyota 9015, and Seiko NH35 / NH36 helps show why movement diameter, height, stem position, rotor clearance, and caseback architecture must be considered before the external case shape is finalised.

The SW300-1 shares a similar broad diameter class with several Swiss 11½-ligne automatic movements, but its 3.60 mm movement height places it in a slim automatic category.

That distinction is central to the case-design problem.

The SW300-1 is not simply a smaller SW200-1.

It is a different vertical packaging opportunity.

SW300-1 Compared With Other Common Movements

Technical Source Classification

The following hierarchy applies throughout this page.

Level A — Direct Manufacturer Specification
Level B — Manufacturer Drawing Interpretation
Level C — Execution-Dependent Manufacturer Information
Level D — HorologyCAD Engineering Interpretation
Level E — Project-Specific Validation

Level A means a value stated explicitly in official Sellita documentation.

Level B means a dimension or relationship read directly from an official Sellita technical drawing.

Level C means a value or relationship that may change according to movement execution, date arrangement, no-date execution, dial configuration, hand-fitting height, supplied stem, or casing components.

Level D means case-design guidance developed from manufacturer information and movement-led engineering principles.

Level E means a relationship requiring confirmation through selected components, physical measurements, tolerance analysis, prototype assembly, functional testing, or production inspection.

Level D and Level E information must not be represented as official Sellita specifications.

Manufacturer Data Register

Data item	Manufacturer reference	Source class
Calibre	SW300-1	Level A
Movement family	SW300	Level A / C
Case-fitting diameter	25.60 mm	Level A / B
Movement height	3.60 mm	Level A
Frequency	28,800 A/h / 4 Hz	Level A
Jewel count	25	Level A
Running time	42 hours in older technical documentation; later/current executions may differ	Level A / C
Balance lift angle	51°	Level A
Display	Central hours, minutes, seconds; date or no-date depending on execution	Level A / C
Winding	Automatic and manual	Level A
Stop seconds	Yes	Level A
Fine timing device	Yes in documented technical references	Level A
Oscillating weight	Central rotor with ball-bearing support	Level A / B
Setting-stem positions	Execution dependent	Level A / C
Casing components	Execution dependent	Level B / C
Dial fastening	Execution dependent	Level B / C
Date or no-date execution	Execution dependent	Level C
Hand-fitting height	Execution dependent	Level C
Movement-holder strategy	Project specific	Level D / E
Finished case cavity	Project specific	Level D / E
Rotor clearance allowance	Project specific	Level D / E
Crown-tube position	Derived from movement stem axis and case datum system	Level B / D / E

Every numerical value used in released production CAD should be checked against:

applicable drawing page
document revision
exact movement execution
drawing convention
stated tolerance
physical movement sample where practical

Where a drawing is unclear, an inference should not be presented as confirmed manufacturer data.

Record Before Beginning CAD

Before developing the case, create a project-specific movement record.

Record:

manufacturer
calibre
physical movement marking
movement grade
supplier
purchase date
date or no-date execution
hand-fitting-height code
dial specification
dial thickness
dial attachment
intended hand set
setting-stem option and reference
selected casing clamp
clamp bend and length
clamp screw type
movement-holder strategy
crown type
crown-tube architecture
manufacturer-document revision
physical measurements
known component deviations
CAD revision
prototype revision

A movement should not be represented only by a vague project label such as “SW300 case.”

The project record should identify the exact movement and component configuration around which the case is being developed.

Why the SW300-1 Matters

The SW300-1 occupies an important position in practical slim Swiss automatic watchmaking.

Its value does not come from being exotic.

It comes from offering:

Swiss automatic architecture
a slim 3.60 mm movement height
a familiar 11½-ligne diameter class
modern 4 Hz operation
automatic and manual winding
stop-seconds functionality
date and no-date possibilities depending on execution
premium movement positioning
service familiarity
suitability for refined independent watches
strong relevance to ETA 2892-A2-style case architecture

The SW300-1 is frequently selected because it gives a designer the opportunity to reduce finished case thickness while retaining a conventional central-rotor automatic layout.

That opportunity is real.

It is not automatic.

Poor SW300-1 integration can produce:

unnecessary finished thickness
rotor contact
weak caseback stiffness
poor crown and stem alignment
rough winding
poor setting feel
weak movement retention
date-window misalignment
dial displacement
insufficient hand clearance
fragile crown-tube support
compromised sealing
difficult assembly
poor service access

A correctly integrated SW300-1 can produce a watch that feels refined, slim, controlled, and professionally resolved.

The difference lies in the surrounding architecture.

Sellita and the SW300 Family

The SW300 family belongs to Sellita’s slim automatic movement category.

Sellita is a Swiss movement manufacturer based in La Chaux-de-Fonds, an important centre of Swiss watchmaking. The company became especially important to the wider watch industry as independent and non-integrated brands sought reliable Swiss mechanical movements outside fully in-house production.

Within that context, the SW300 family provides a slim Swiss automatic option for brands requiring a lower-profile movement architecture than standard-height automatic calibres.

The SW300-1 should be understood as a slim automatic platform.

It should not be described merely as a thinner SW200-1.

The SW200-1 and SW300-1 occupy different vertical packaging categories:

the SW200-1 represents standard-height Swiss automatic architecture
the SW300-1 represents slim Swiss automatic architecture

This distinction matters because movement height affects:

finished case thickness
caseback depth
rotor clearance
dial-side packaging
hand-to-crystal clearance
crown-tube position
structural wall allocation
movement-holder design
sealing architecture
caseback stiffness

The SW300-1 allows thinner watch-case architecture only when these relationships are deliberately controlled.

Current Calibre Status

This page covers the Sellita SW300-1.

The SW300 family includes multiple related executions and derivative movement families.

Some related movements may include:

date executions
no-date executions
GMT variants
small-seconds variants
skeletonised executions
other display or complication-based derivatives

These related movements may alter:

total height
dial-side geometry
hand stack
crown settings
caseback requirements
movement-holder geometry
date or display position

The existence of a movement family does not imply automatic interchangeability.

Every execution requires its own technical review.

An SW300-1 project must be validated against SW300-1 documentation and the actual movement supplied for the project.

Movement Architecture

The documented SW300-1 execution provides:

central hours
central minutes
central seconds
date through a window in the documented date execution
quick date correction in the documented date execution
automatic winding
manual winding
stop seconds
fine timing device
central oscillating weight
ball-bearing rotor support
conventional dial-side hand and calendar architecture

The architecture is slim.

It is not mechanically simple from a case-design standpoint.

The case designer must coordinate:

overall movement envelope
case-fitting diameter
stepped movement geometry
locating surfaces
holder or casing ring
casing clamps
dial attachment
date display where applicable
selected hand stack
setting stem
keyless works
crown tube
crown
rotor envelope
caseback
caseback stiffness
rehaut
crystal
gaskets

The SW300-1 is selected partly because it is thin.

That makes careless case design more visible, not less important.

SW300-1 Movement Architecture Diagram

Movement Grades and Timing Performance

Sellita identifies movement-grade and timing-performance distinctions in its technical documentation and supply structure.

Movement grade should not be confused with movement variant.

A grade principally concerns:

regulation
positional performance
quality-control limits
component selection
finishing
commercial positioning

A movement variant or execution may affect physical case integration through:

calendar arrangement
no-date configuration
hand-fitting height
display system
dial geometry
supplied casing components

Manufacturer timing criteria are useful for:

movement specification
procurement
quality control
regulation expectations
final product positioning

They do not change the basic case-design requirement to control the 25.60 mm case-fitting diameter, 3.60 mm movement height, rotor clearance, stem axis, and dial-side stack.

The exact grade should nevertheless be recorded in the project movement register.

Appropriate Applications and Limitations

The SW300-1 offers a practical balance of:

Swiss manufacture
slim automatic architecture
serviceability
supplier relevance
premium positioning
familiar 11½-ligne format
modern 4 Hz operation

It is particularly appropriate for:

slim automatic watches
refined sports watches
premium dress watches
lower-profile dive watches
compact Swiss automatic cases
premium independent watches
watches where Swiss movement positioning matters
designs where finished case thickness is a central objective

It is less naturally suited to projects centred on:

lowest possible movement cost
very large tool-watch architecture where slimness provides little benefit
cases where structural stiffness cannot be preserved
projects where a thicker, cheaper, or more robust workhorse calibre is more appropriate
designs where the thin movement is offset by an unnecessarily deep caseback, tall dial-side stack, or thick crystal system

These are application boundaries rather than defects.

The movement should be selected because it suits the intended watch architecture.

Movement thinness cannot compensate for weak case integration.

From Manufacturer Data to Case Architecture

Manufacturer documentation tells the designer what the movement is.

It does not completely determine how the watch case should be built.

The case designer must still establish:

locating datums
cavity strategy
holder geometry
casing-clamp use
radial clearance
anti-rotation
axial retention
stem-axis transfer
crown-tube geometry
rotor protection
caseback depth
caseback stiffness
dial support
hand clearance
crystal clearance
sealing
tolerances
assembly
inspection
service removal

The central HorologyCAD principle is:

A movement dimension becomes useful only when its role within the complete watch system is understood.

SW300-1 Casing Envelope

Sellita’s SW300-1 technical documentation identifies the movement as a three-dimensional casing system rather than a single simple cylinder.

The principal headline dimensions are:

25.60 mm case-fitting diameter
3.60 mm movement height
11½-ligne size class

These dimensions serve different functions.

The 25.60 mm dimension identifies the principal manufacturer casing-fit reference.

The 3.60 mm height describes the movement itself, not the finished watch stack.

The finished case cavity should therefore not be represented as one unsupported cylindrical diameter.

The designer must determine:

which feature locates the movement
which regions require clearance
which surface establishes the support plane
how the holder or clamps interact with the case
how the movement enters and leaves the case
how the dial and hands sit above the movement
how the rotor is protected below the movement
how the crown tube is aligned from the stem axis

The SW300-1’s thinness makes this more important, not less.

A slim movement leaves less room for careless packaging.

Related engineering reference: Internal Case Geometry & Movement Cavity Sizing

SW300-1 Internal Case Envelope Diagram

Movement Diameter and Internal Case Geometry

The 25.60 mm case-fitting dimension establishes a manufacturer casing reference.

It does not automatically establish the finished case-cavity diameter.

The internal case may also need to accommodate:

movement holder
casing ring
locating shoulders
casing clamps
clamp screws
radial assembly clearance
coating or finishing buildup
anti-rotation features
inspection access
service-tool access

A cavity modelled directly at the nominal movement dimension may become difficult or impossible to assemble after manufacturing variation is introduced.

It may also apply uncontrolled force to the movement or holder.

The designer must define:

which component contacts the case
which surface establishes concentricity
which feature limits radial movement
which feature prevents rotation
how the movement enters the case
how the movement is removed for service

The objective is not merely to make the movement fit.

The objective is to locate it predictably.

Related engineering reference: Internal Case Geometry & Movement Cavity Sizing

Radial Clearance and Movement Location

Radial clearance is the controlled allowance between the locating components of the movement system and the surrounding case structure.

The relevant interface may be:

movement to case
movement to holder
holder to case
casing ring to case
clamp system to case

The correct allowance depends on:

holder architecture
component material
machining method
surface finish
coating
dimensional tolerance
assembly method
inspection strategy
service requirements

Insufficient clearance can produce:

difficult insertion
forced seating
movement or holder distortion
stem-axis displacement
dial displacement
date-window displacement
surface damage
dependence on hand fitting

Excessive clearance can produce:

radial movement
rotation
date-window displacement
dial movement
stem side loading
inconsistent crown feel
overdependence on clamps

There is no responsible universal cavity addition suitable for every SW300-1 case.

Clearance must be allocated to a defined interface within a defined architecture.

Related engineering reference: Radial Clearance

Anti-Rotation Control

Radial location and rotational control are separate functions.

A circular cavity may establish approximate concentricity while still permitting movement or holder rotation.

Rotation can affect:

stem alignment
crown function
dial position
date-window alignment
hand alignment
clamp loading
assembly consistency

Anti-rotation may be provided through:

movement-holder geometry
casing clamps
keyed features
locating tabs
dedicated case geometry

The setting stem must not be treated as a structural anti-rotation pin.

The stem is an operating component.

It is not a substitute for movement retention.

Movement Height and Finished Watch Thickness

The SW300-1 movement height is 3.60 mm.

That dimension represents only one part of the complete watch stack.

Finished thickness must also account for:

movement seating
dial support
dial thickness
hand-fitting height
hand-to-hand clearance
hand-to-crystal clearance
rehaut depth
crystal thickness
crystal retention
rotor clearance
caseback internal depth
caseback wall thickness
caseback stiffness
gasket compression
movement retention
manufacturing variation
finishing variation

A case designed around the movement height alone will usually be incorrect.

Potential consequences include:

rotor contact
hand contact
movement compression
weak caseback construction
excessive caseback depth
greater finished thickness than expected
incorrect crown-axis position
compromised sealing geometry

A well-proportioned SW300-1 case is possible.

The complete axial stack must be resolved before the exterior thickness is fixed.

Related engineering reference: Movement Height vs Case Thickness

Axial Stack Control

The axial stack controls the vertical relationship between:

caseback
rotor
movement
movement seat
dial
hands
rehaut
crystal

The SW300-1 is often chosen because the designer wants a thinner finished watch.

That creates pressure to compress the stack.

The caseback side must provide free operating space for the automatic winding system.

The dial side must provide controlled support and clearance for the dial and hands.

Insufficient axial space can cause:

rotor rubbing
hand contact
dial loading
movement compression
caseback interference
reduced winding efficiency

Excessive uncontrolled space can cause:

movement lift
dial movement
stem misalignment
retention inconsistency
impact noise
variable crown operation

Axial clearance is not arbitrary empty space.

It is a controlled relationship between real surfaces and their tolerance limits.

Related engineering reference: Axial Clearance

SW300-1 Axial Stack Diagram

Rotor Clearance and Caseback Architecture

The rotor occupies a moving envelope behind the movement.

The caseback cannot be developed only from the desired exterior profile.

Its internal geometry must preserve rotor clearance through:

movement seating variation
rotor motion
rotor endshake
manufacturing tolerance
caseback deflection
gasket compression
finishing buildup
shock loading

Insufficient clearance can cause:

rubbing
scraping noise
winding drag
reduced winding efficiency
witness marks
wear debris
movement damage

A common SW300-1 mistake is to assume that the reduced movement height removes rotor risk.

It does not.

The rotor still requires protected space.

A thin movement can still be paired with a poorly designed caseback.

The rotor space should be resolved before the external caseback profile is finalised.

The caseback must then satisfy several requirements simultaneously:

rotor protection
structural stiffness
gasket support
thread or retention geometry
service access
acceptable external proportion

Related engineering reference: Rotor Clearance Requirements

Caseback Stiffness in a Slim Watch

The SW300-1 allows the designer to reduce internal stack height.

That should not be interpreted as permission to reduce the caseback to an inadequately supported shell.

A thin caseback must still resist:

external pressure
assembly load
gasket compression
thread loading
local deformation
impact
bending toward the rotor

Caseback stiffness depends on:

material
wall thickness
internal span
exterior curvature
thread geometry
gasket position
machining features
display-back construction where applicable

A caseback that deflects can reduce rotor clearance even when the nominal CAD gap appears sufficient.

The rotor envelope must therefore be protected under realistic structural conditions, not only in the undeformed model.

This is one of the defining SW300-1 case-design problems:

the movement allows thinness, but the caseback must still behave like an engineered structure.

Winding and Functional Test Information

The SW300-1 supports automatic and manual winding.

Sellita technical documentation provides controlled winding and test information for workshop and production use.

These instructions relate to:

manual winding through the stem
testing with the automatic winding system installed
testing without the automatic system installed
testing with the self-winding system

These are servicing and controlled-test procedures rather than everyday user instructions.

For the case designer, the important implications are:

the crown and stem system must permit smooth manual winding
the setting stem must remain aligned throughout operation
the crown must provide suitable access
the keyless works must not receive lateral load
the rotor must remain free to operate
the caseback must not introduce automatic-winding interference

A case can satisfy nominal movement dimensions and still compromise winding performance through poor stem alignment or insufficient rotor clearance.

Stem Axis and Crown-Tube Alignment

The crown position must be derived from the movement stem axis.

It should not be selected visually and joined to the movement afterward.

The stem axis controls:

case-wall bore position
crown-tube centreline
crown seating
winding feel
setting feel
date correction where applicable
keyless-works loading
crown-gasket alignment
crown-guard geometry
case-wall material around the tube

The reduced vertical architecture of an SW300-1 case makes stem-height errors especially visible.

There is less unused internal volume available to hide a poorly placed crown axis.

If the crown tube is misplaced, the stem may be forced into alignment during assembly.

The watch may still operate, but the system can suffer from:

stem bending
rough winding
poor setting feel
keyless-works side load
uneven gasket compression
crown-tube wear
premature failure
visibly incorrect crown position

The movement support plane, stem axis, case-wall bore, crown tube, and crown should be developed as one mechanical chain.

The crown is both:

a user interface
a sealing interface

Related engineering reference: Crown and Stem Alignment in Watch Cases

Stem Height and Crown-Tube Position

Stem height is one of the most important movement-led case dimensions.

For the SW300-1, the stem axis must be interpreted from the relevant technical drawing convention and transferred into the case datum system correctly.

The designer must define:

movement support plane
movement seating level
stem centreline
case-tube bore height
crown-tube shoulder
crown seat
gasket relationship
external crown centreline
remaining structural material around the tube

Small stem-height errors can cause large practical problems.

The watch may still assemble, but:

crown operation may feel rough
the stem may drag
the keyless works may receive side load
the crown gasket may compress unevenly
the crown may sit visibly high or low

A correct SW300-1 case uses the stem axis as a datum.

The exterior crown position is designed around that datum.

Related engineering reference: Stem Height to Crown Tube Position Relationship

Date, No-Date, and Dial Interface

The SW300-1 may be encountered in date or no-date executions depending on the selected movement and supplier configuration.

The exact execution matters.

A date-equipped SW300-1 requires coordination of:

date-wheel location
dial aperture
date correction
rotational movement position
rehaut opening
chapter-ring position
crown settings

A no-date execution removes the date display and related dial aperture.

It does not remove the need for:

exact movement identification
correct stem interpretation
rotor clearance
movement retention
dial-side stack validation
casing verification

The dial side must be coordinated with:

movement location
dial seat
case opening
date aperture where applicable
rehaut
chapter ring
crystal
hand stack

Important dial constraints include:

dial-seat diameter
support geometry
dial thickness
dial-fixing arrangement
date-window position
movement rotational position
rehaut depth
chapter-ring clearance
hand-stack height
crystal underside clearance
visual centring

The dial is not merely a decorative disc above the movement.

It is part of the axial stack and the visible movement-location system.

If the movement shifts radially or rotationally, a date display may misalign.

If the dial seat is incorrect, the dial may sit too high, too low, or without adequate support.

The dial-side architecture should be resolved before final case thickness and crystal position are declared.

Related engineering reference: Dial Integration & Case Interface

Dial Attachment

The Sellita documentation identifies manufacturer dial-fastener references within the movement system.

The final dial programme must confirm:

attachment method
locking geometry
engagement
dial thickness
date-disc clearance where applicable
service release method

The case should not compensate for an incorrectly specified dial.

Movement, dial, and case should be developed as one coordinated assembly.

Changes to dial thickness, attachment position, applied markers, dial construction, or surface build-up may alter the axial stack or assembly process.

Hand-Fitting Heights and Crystal Clearance

The selected hand-fitting execution changes the dial-side stack.

The SW300-1 case must provide clearance for:

hour hand above the dial
minute hand above the hour hand
seconds hand above the minute hand
seconds hand below the crystal
hand-fitting variation
dial-thickness variation
hand flex
shock displacement
crystal-position variation
manufacturing tolerance

A case can have correct movement diameter, radial location, rotor clearance, and crown alignment and still fail at the hand stack.

Possible failures include:

hour hand contacting the dial
minute hand contacting the hour hand
seconds hand contacting the minute hand
seconds hand contacting the crystal
hand tips contacting the rehaut
inadequate shock allowance

The highest operating hand should be treated as a dynamic upper boundary.

The crystal underside must remain clear under expected tolerance and operating conditions.

This is particularly important in a slim watch because dial-side clearance may be reduced aggressively.

Related engineering references: Hand Stack Height and Clearance Requirements and Dial to Crystal Clearance

Detailed Hand-Height Data

The complete manufacturer hand-height and dial-side data should be made available through:

an expandable technical-reference section
a separate HorologyCAD reference table
direct consultation of the official Sellita document

The main article should identify the need to confirm the exact hand-fitting execution without overwhelming the introductory specification layer.

Movement Holder and Retention Strategy

The SW300-1 must be retained securely without being:

distorted
pinched
allowed to shift
allowed to rotate
compressed by the caseback

A complete retention system should control:

radial movement
axial movement
rotation
dial alignment
stem loading
shock response
service removal

Possible strategies include:

manufacturer-style casing clamps
dedicated movement holder
casing ring
spacer ring
locating shoulders
combined locating and retention geometry

The correct method depends on:

case material
machining method
production quantity
assembly order
water-resistance target
dial architecture
service strategy

The movement should not be trapped accidentally between the dial side and caseback.

The caseback should not become the sole retention feature unless the full axial stack has deliberately been engineered for that role.

Retention must be controlled.

It should not depend on unknown compression.

Related engineering reference: Movement Securing Methods

Setting-Stem Removal and Service Access

A professional SW300-1 case must allow the movement to be installed, tested, removed, and recased without damage.

Service access should be considered during CAD development, not after the first prototype has already been machined.

The case architecture should provide:

visible access to required release points
sufficient tool approach
adequate clearance around the movement
stable support during stem removal
access to clamps or holder features
a service sequence that avoids levering against finished surfaces

The release point and retention features should not be hidden behind:

an inaccessible holder
a case-wall obstruction
a casing clamp
a decorative internal feature
an assembly sequence that traps the movement

A case may hold the movement securely and still be poorly engineered if the movement cannot be removed safely.

Service access must be reviewed during CAD development.

Sealing and Water-Resistance Architecture

Water resistance must be integrated into the movement-led case architecture from the beginning.

The case must coordinate:

crown sealing
crown-tube alignment
caseback sealing
crystal sealing
gasket compression
thread engagement
sealing-surface finish
structural stiffness
axial-stack behaviour
service replacement

Thin-case architecture can reduce the material available around:

crown-tube supports
gasket grooves
crystal seats
caseback threads
retaining shoulders
sealing surfaces

The designer must avoid sacrificing:

caseback stiffness
crown-tube support
crystal-seat rigidity
gasket-groove integrity
thread depth
sealing-surface width
internal shoulder strength

A misaligned crown tube can compromise crown feel and gasket function simultaneously.

A shallow caseback can compromise rotor clearance or gasket behaviour if the internal architecture has not been resolved.

Water resistance is not added after movement fit is complete.

It is part of the same engineering system.

Related engineering references: Water Resistance Engineering in Watch Cases and Caseback Sealing System

Case Rigidity and Thinness

The SW300-1 makes thinner case architecture possible.

It does not remove structural requirements.

A thin case must still preserve adequate rigidity around:

mid-case walls
crown-tube bore
crystal seat
bezel interface
caseback thread
gasket grooves
movement-locating shoulders
lug junctions

Reducing material without considering load paths can produce:

case distortion
sealing-surface movement
thread weakness
crown-tube instability
crystal-seat deformation
reduced impact resistance
rotor-clearance loss under deflection

The correct objective is not the smallest possible dimension at every point.

The objective is an efficient structure in which material is retained where it performs a mechanical function.

Slimness should result from controlled packaging, not structural neglect.

Manufacturing and Tolerance Strategy

A CAD model can appear correct while remaining difficult or impossible to manufacture consistently.

The case architecture must account for:

tool access
cutter radius
bore accuracy
concentricity
flatness
perpendicularity
thread geometry
finishing removal
coating buildup
inspection method
component variation
assembly variation

Every critical interface should have:

nominal dimension
tolerance
functional purpose
inspection method

The designer should be able to explain:

what locates the movement
what retains it
what prevents rotation
what controls the stem axis
what protects the rotor
what supports the dial
what establishes hand clearance
what compresses each gasket
how each relationship will be inspected

If a critical feature cannot be measured or inspected, its production control is weak.

A slim case has less unused volume available to absorb uncontrolled variation.

Large safety allowances added late in the design process can remove the thickness advantage of the SW300-1.

The objective is not to eliminate all clearance.

The objective is to allocate clearance and tolerance deliberately where mechanically required.

Related engineering references: Watch Case Tolerances and CNC Machining Constraints in Watch Cases

Manufacturing Suitability

The SW300-1 is highly suitable for refined slim automatic watch production when the case is engineered correctly.

Use case	Suitability	Reason
CNC prototyping	Good to excellent	Slim architecture requires disciplined stack control
Low-volume production	Good to excellent	Strong modern Swiss movement option where sourcing is controlled
Independent brands	Excellent	Supports premium Swiss positioning and refined proportions
First serious mechanical project	Moderate	Less forgiving than larger or thicker entry-level movements
Slim automatic watches	Excellent	3.60 mm height supports lower-profile architecture
Premium dress watches	Excellent	Slim Swiss movement suits restrained proportions
Refined sports watches	Excellent	Strong balance of thinness and automatic functionality
Lower-profile dive watches	Good to excellent	Suitable where rotor clearance and sealing are controlled
Haute horology context	Moderate	Strong base calibre, but finishing, modification, and broader product context matter

The SW300-1 is technically capable and packaging-efficient, but it is not casual to integrate.

It rewards disciplined engineering and exposes poor tolerance control, especially around:

axial stack
rotor clearance
caseback stiffness
crown alignment
hand clearance
sealing geometry
movement retention

Service Ecosystem and Long-Term Use

The SW300-1 benefits from Sellita production relevance and a familiar Swiss automatic servicing context.

It is suitable for watches intended to be:

maintained
regulated
repaired
recased
retained long term

Serviceability also imposes case-design requirements.

A well-resolved case should permit:

controlled stem removal
access to retention features
holder or clamp removal
non-destructive movement extraction
caseback servicing
gasket replacement
reliable recasing
functional checks after assembly

A case that cannot be serviced cleanly is not fully engineered.

Thinness should never depend on making routine service access difficult or destructive.

Collector and Product Perception

Collectors generally understand the SW300-1 as a slim Swiss automatic movement with a stronger technical position than standard workhorse calibres where case thickness matters.

It is recognised for:

reduced movement height
premium case potential
modern Sellita production
Swiss movement positioning
relationship to ETA 2892-A2-style architecture
suitability for refined automatic watches

That perception can be strengthened or weakened by the finished watch.

In a poorly designed case, the movement’s thinness may be wasted by:

excessive caseback depth
a tall rehaut
thick crystal architecture
poor crown alignment
weak finishing
poor movement integration

In a well-engineered watch, the SW300-1 can feel like the correct movement for the design:

slim
refined
technically appropriate
maintainable
professionally integrated

The movement provides a slim Swiss foundation.

The case determines whether that foundation feels properly used.

Known Weaknesses and Trade-Offs

The SW300-1 is a strong movement, but it is not ideal for every project.

Its trade-offs include:

higher cost than common entry-level movements
greater sourcing complexity than broadly available Japanese calibres
premium expectations placed on the finished watch
reduced tolerance margin in aggressively thin cases
continued need for rotor clearance
execution-specific date and power-reserve considerations
limited benefit where the surrounding case remains thick
structural risks if thinness is pursued without adequate material

These characteristics do not make the SW300-1 a poor movement.

They define where the surrounding watch must work harder.

A successful SW300-1 watch should rely on:

controlled slim-case architecture
disciplined movement integration
good crown feel
strong structural design
appropriate dial and crystal proportions
finishing quality
serviceability
coherent engineering

It should not rely on the movement name alone.

Relationship to the ETA 2892-A2

The Sellita SW300-1 is commonly positioned in the same broad slim Swiss automatic category as the ETA 2892-A2.

The comparison is useful because both movements share:

a similar 11½-ligne movement class
slim automatic architecture
central rotor winding
three-hand display
premium case-thickness potential

From a case-design perspective, both require careful control of:

slim axial-stack height
automatic rotor clearance
caseback depth
crown and stem alignment
movement securing
dial-side stack planning
thin-case rigidity
sealing geometry
manufacturing tolerance

This does not mean they should be treated as automatically identical.

The final case must always be checked against:

the exact movement
the exact technical drawing
hand-height execution
dial system
date configuration
holder arrangement
current manufacturer data

Similar dimensions do not guarantee complete casing interchangeability.

SW300-1 Ecosystem and Related Movements

The SW300-1 should be understood within a broader movement ecosystem that may include:

ETA 2892-A2 — a historically important slim Swiss automatic reference point
Sellita SW300-1 — the calibre covered by this page
Sellita SW330 family — related GMT architecture requiring separate validation
Sellita SW360 family — related small-seconds architecture requiring separate validation
Sellita SW200-1 — standard-height Sellita automatic architecture
ETA 2824-2 — standard-height Swiss automatic architecture

Similar naming, similar function, or similar nominal diameter does not prove casing compatibility.

The word “compatible” should never replace dimensional verification.

What the SW300-1 Does Not Decide

The movement does not define:

final case diameter
bezel design
lug geometry
case-wall thickness
crown shape
crown-tube installation
caseback profile
gasket selection
crystal system
rehaut depth
dial opening
finishing specification
machining strategy
external proportion

A slim movement reduces one category of packaging difficulty.

It does not replace case engineering.

The movement establishes the internal reference.

The designer must convert that reference into:

controlled geometry
tolerance behaviour
assembly logic
inspection criteria
prototype validation
repeatable production architecture

Common SW300-1 Case-Design Mistakes

Assuming 3.60 mm movement height automatically creates a thin watch

Movement height excludes dial, hands, crystal, rotor clearance, caseback, sealing, and structural material.

Treating 25.60 mm as the finished cavity diameter

The case-fitting diameter is a manufacturer reference, not a complete finished case cavity.

Reducing caseback depth without checking the rotor

The automatic rotor still requires protected operating clearance.

Reducing caseback thickness without checking stiffness

A thin caseback can deflect toward the rotor even when nominal CAD clearance looks sufficient.

Positioning the crown visually

The crown tube must be positioned from the movement stem axis.

Forcing the stem into alignment

A watch can operate while the stem and keyless works are already being side-loaded.

Ignoring date-window position where applicable

Small radial or rotational errors can create obvious date-window displacement.

Treating the dial as independent from movement position

The dial is part of the visible movement-location system.

Failing to validate hand-to-crystal clearance

A slim dial-side stack can fail even if the movement fits perfectly.

Reducing crystal clearance too aggressively

The highest operating hand needs tolerance and shock allowance.

Using the caseback to crush or trap the movement

Retention should be deliberate and repeatable.

Assuming SW300-1 and ETA 2892-A2 cases are automatically interchangeable

Similar architecture does not prove complete casing compatibility.

Ignoring machining and finishing allowance

A correct nominal CAD model may become wrong after real manufacturing variation.

Adding gasket geometry after the case has been designed

Sealing affects wall thickness, axial stack, threads, and crown alignment.

Using late-stage safety margins that destroy the thin-case advantage

Slimness must be engineered from the beginning, not recovered at the end.

Designing without an assembly sequence

A component can fit in CAD but remain impossible to install or service.

Treating one successful prototype as production proof

A working prototype demonstrates possibility.

Production requires repeatability.

CAD Difficulty Assessment

The SW300-1 can appear simple in CAD because its headline dimensions are compact and familiar.

That impression is misleading.

A basic visual representation is relatively straightforward.

A professional, manufacturable, serviceable, and tolerance-aware SW300-1 case is considerably more demanding.

Task	Approximate difficulty
Basic conceptual movement placement	3/10
Controlled slim automatic case layout	6/10
Professional movement-fit case architecture	8/10

The main difficulty lies in:

radial tolerance
movement location
crown feel
stem alignment
rotor clearance
caseback depth
caseback stiffness
dial-side stack control
sealing geometry
structural wall control
repeatable assembly
service access

A beginner can place the SW300-1 inside a circular cavity.

A professional case design defines how the movement is located, protected, sealed, retained, and serviced while preserving the advantage of its reduced height.

Physical-Sample Validation

Manufacturer documentation establishes the nominal technical basis.

Physical inspection confirms the actual components entering the project.

Before final CAD release, compare the documentation with:

physical SW300-1 movement
selected dial
intended hand set
setting stem
crown
crown tube
casing clamps
movement holder
prototype components

Where practical, inspect:

movement envelope
case-fitting region
movement height
stem-axis relationship
setting-stem positions
rotor envelope
dial interface
clamp geometry
hand-height execution

Physical measurements should not casually override official drawings.

Measurement uncertainty, access limitations, and component condition must be considered.

Where the drawing, supplier information, and physical component appear to disagree:

stop the design release
identify the discrepancy
verify document revision
confirm movement execution
consult the supplier or manufacturer where necessary
record the resolution

An unresolved discrepancy should not be hidden inside an arbitrary clearance.

SW300-1 Pre-Prototype Verification Checklist

Before releasing the case for prototyping, confirm that:

physical calibre is identified as SW300-1
exact execution is recorded
technical-document revision is recorded
applicable 25.60 mm casing fit is identified
3.60 mm movement height is understood as movement height only
date or no-date arrangement is confirmed
hand-fitting-height execution is confirmed
dial specification is confirmed
dial attachment is confirmed
date aperture is coordinated where applicable
setting-stem option is confirmed
crown system is confirmed
locating datum is defined
radial locating interface is defined
holder or casing-ring system is defined
clamp type and screw are defined where applicable
stem-release access is preserved
anti-rotation control is defined
radial tolerances are assigned
axial tolerances are assigned
rotor clearance is protected
caseback clearance is checked at worst case
caseback stiffness is reviewed
stem axis is transferred into the case datum system
crown-tube alignment is verified
crown positions are verified
dial-seat height is controlled
hand-to-hand clearance is protected
hand-to-dial clearance is protected
hand-to-marker clearance is protected
hand-to-rehaut clearance is protected
hand-to-crystal clearance is protected
movement lift is controlled
movement rotation is controlled
gasket compression does not compromise movement clearance
machining allowances are included
finishing allowances are included
inspection methods exist
assembly order has been reviewed
service removal is possible
physical-sample inspection is recorded
representative production components will be used in the prototype

This checklist does not replace production drawings or prototype testing.

It controls the principal SW300-1 movement-to-case risks before manufacture begins.

Movement-Led SW300-1 Case-Design Workflow

Confirm the movement.

Identify the exact calibre, execution, date or no-date arrangement, grade, hand height, and supplied components.

Secure the official documentation.

Record the document title, revision, date, and source.

Create the project movement record.

Record the physical marking, supplier, dial, hands, stem, holder, clamps, and crown system.

Extract manufacturer geometry.

Review the 25.60 mm case-fitting reference, 3.60 mm movement height, dial interface, setting-stem information, automatic-winding architecture, and casing references.

Inspect the physical components.

Compare the actual movement and selected parts against the documented specification.

Select the locating architecture.

Define which component establishes position.

Resolve radial fit.

Allocate clearance and tolerance at the selected locating interface.

Resolve anti-rotation.

Provide rotational control independent of the setting stem.

Resolve the axial stack.

Build the complete stack from caseback to crystal.

Protect the rotor.

Resolve internal caseback geometry before fixing the exterior profile.

Review caseback stiffness.

Confirm that the caseback remains structurally adequate and does not deflect into the rotor envelope.

Transfer the stem axis.

Position the case-wall bore and crown tube from the movement datum system.

Resolve the crown system.

Establish stem length, operating positions, tube projection, crown seating, and gasket behaviour.

Resolve dial and hands.

Coordinate dial seat, date aperture where applicable, selected hand height, rehaut, and crystal.

Define retention.

Control radial movement, axial lift, and rotation without distorting the movement.

Preserve service access.

Ensure that stem release, holder, clamps, and removal sequence remain practical.

Integrate sealing.

Coordinate crown, crystal, and caseback sealing with the existing architecture.

Apply tolerances.

Assign tolerances and inspection methods to all critical interfaces.

Validate assembly and service.

Confirm that the watch can be assembled, opened, and serviced without damage.

Build and inspect the prototype.

Use representative components and record deviations from CAD.

This sequence prevents the common mistake of selecting a thin movement, drawing an attractive low-profile exterior, and only later discovering that rotor clearance, hand clearance, crown alignment, structural stiffness, or sealing geometry has been compromised.

Related engineering reference: Movement to Case Fit

Prototype Validation

The first prototype is an engineering test article.

After assembly, verify that:

movement enters without forced seating
holder or casing ring remains undistorted
casing clamps seat correctly where used
clamp screws remain accessible where used
stem-release access remains accessible
movement cannot shift radially
movement cannot rotate
movement cannot lift axially
stem enters without lateral deflection
winding is smooth
time setting is smooth
date correction operates correctly where applicable
crown positions are distinct
dial remains centred
date aperture remains aligned where applicable
hands clear one another
hands clear the dial
hands clear applied markers
hands clear the rehaut
hands clear the crystal
rotor rotates freely
no caseback witness marks appear
no abnormal rotor noise is present
caseback sealing does not reduce rotor clearance
caseback stiffness is acceptable
crown and crystal sealing function as intended
case can be reopened
movement can be removed
movement can be recased repeatably

Where appropriate, repeat checks:

dial up
dial down
crown up
crown down
before final caseback tightening
after final assembly
after sealing tests
after reopening and recasing

Prototype Measurement Record

For each prototype, record:

prototype revision
CAD revision
technical-document revision
movement identification
movement grade
date or no-date execution
dial identification
hand-set identification
hand-height execution
crown and tube identification
stem option
holder or clamp revision
radial-interface measurement
movement seating position
caseback clearance
caseback stiffness observation
dial position
date-window alignment where applicable
hand clearances where practical
winding observations
setting observations
sealing-test result
failed checks
corrective action
final disposition

Possible dispositions include:

accepted
accepted with controlled deviation
rework required
redesign required
rejected

A prototype should not be accepted merely because it can be assembled.

Acceptance requires correct location, free operation, serviceability, structural adequacy, and conformity with the intended engineering requirements.

Production Acceptance Criteria

Before approving the architecture for production, confirm that:

critical dimensions have tolerances
tolerances reflect the manufacturing process
inspection methods exist
worst-case conditions have been reviewed
movement installation is repeatable
movement retention is repeatable
stem access is repeatable
crown function is repeatable
rotor clearance is repeatable
caseback stiffness is repeatable
dial and date alignment are repeatable where applicable
hand clearance is repeatable
sealing is repeatable
disassembly and recasing are repeatable
approved deviations are documented
production samples match the approved prototype

One successful prototype proves possibility.

Production approval requires repeatability.

Related HorologyCAD Engineering Pages

Continue through the movement-led case-design system.

Start With Movement Fit

Movement Selection
Movement to Case Fit
Internal Case Geometry & Movement Cavity Sizing

Define Clearance and Case Architecture

Resolve Crown, Stem, Dial, and Hands

Control Retention, Sealing, and Manufacturing

Movement Securing Methods
Water Resistance Engineering in Watch Cases
Caseback Sealing System
Watch Case Tolerances
CNC Machining Constraints in Watch Cases

Continue the SW300-1 Cluster

Sellita SW300-1 Case Design Constraints
Sellita SW300-1 Case Design Guide
Sellita SW300-1 Case Core: Movement-Fit CAD System

Compare With Related Movements

HorologyCAD Design Position

The Sellita SW300-1 is not merely a slim movement specification.

It is a fixed internal engineering system around which the watch case must be developed.

Its case-fitting diameter, movement height, stem axis, dial interface, date or no-date execution, hand-fitting execution, rotor, and retention requirements all influence the finished watch.

When those relationships are interpreted correctly, the designer can create a case that:

assembles predictably
locates the movement accurately
controls rotation
protects the automatic system
aligns the crown and stem
preserves dial and hand clearance
uses the reduced movement height intelligently
supports water resistance
maintains structural stiffness
controls manufacturing variation
can be inspected
remains serviceable

The principle is straightforward:

Begin with verified manufacturer data, establish the internal case architecture, preserve the slim movement advantage through controlled stack design, validate using real components, and develop the exterior around a mechanically resolved system.

Thinness must be engineered.

It cannot be assumed.

Next Step

For the complete movement-to-case relationship:

→ Movement to Case Fit

For movement-cavity sizing and location logic:

→ Internal Case Geometry & Movement Cavity Sizing

For SW300-1-specific failure boundaries:

→ Sellita SW300-1 Case Design Constraints

For the applied SW300-1 design process:

→ Sellita SW300-1 Case Design Guide

Return to HorologyCAD

HorologyCAD is a movement-led watch case design system for developing case architecture around real mechanical movements, manufacturable constraints, and functional assembly requirements.

→ Movement-Led Watch Case Design & Engineering

Technical Note

This page is based on identified Sellita SW300 / SW300-1 technical documentation and current SW300-1 reference checks.

Last checked against identified manufacturer documentation: 22 June 2026.

Manufacturer data should always be checked against the current official Sellita documentation and the exact movement execution used in the project.

HorologyCAD engineering guidance on case geometry, clearance, retention, stem alignment, sealing, assembly, slim-case architecture, caseback stiffness, and validation is interpretive design guidance. Final case architecture should be confirmed against physical components, prototype assembly, and production inspection.