The Sellita SW300-1 is a slim automatic mechanical movement used as a modern reference calibre for thin, movement-led watch case design.
It is important because it sits in the same broad 25.60 mm movement diameter class as the SW200-1 and ETA 2892-A2, but with a slim 3.60 mm height that supports thinner automatic case architecture.
For HorologyCAD, the SW300-1 is useful because it connects directly to ETA 2892-A2-style case design while also supporting modern Sellita-based movement planning.
This page explains the Sellita SW300-1 from a watch case design perspective.
It does not treat the movement as a specification list only.
It explains what the movement dimensions mean for internal case geometry, radial clearance, axial clearance, crown and stem alignment, rotor clearance, caseback depth, dial stack planning, movement securing, and manufacturable case architecture.
For the full site structure, return to the HorologyCAD homepage.
Manufacturer Technical Basis
The Sellita SW300-1 is an 11½ ligne automatic mechanical movement. Published technical references commonly list the SW300-1 with a 25.60 mm case-fitting diameter, 3.60 mm height, 25 jewels, 28,800 vibrations per hour, and automatic winding with central rotor. Sellita technical documentation also identifies the calibre as SW300-1 and lists the technical documentation for the movement family.
Common technical values include:
movement type: automatic mechanical movement
case-fitting diameter: 25.60 mm
height: approximately 3.60 mm
jewels: 25
frequency: 28,800 vph / 4 Hz
power reserve: commonly listed around 42 hours, with some newer versions listed around 56 hours depending on barrel/version
functions: hours, minutes, central seconds, date variants
architecture: slim automatic movement with central rotor
Caliber Corner lists the SW300-1 as 25.6 mm diameter, 3.6 mm thick, 25 jewels, 28,800 bph / 4 Hz, and a 42-hour reserve, while WatchBase lists some SW300-1 variants with a 56-hour typical reserve. This means power reserve should be checked against the exact SW300-1 variant used, while the case-design dimensions remain centred on the 25.60 mm diameter and 3.60 mm height class.
Core Sellita SW300-1 Dimensions
The most important Sellita SW300-1 dimensions for watch case design are:
case-fitting diameter: 25.60 mm
height: approximately 3.60 mm
movement family: slim automatic
ligne size: 11½ ligne
winding: automatic, with hand-winding
frequency: 28,800 vph
jewels: 25
date: variant dependent
central seconds: yes
rotor: yes
For case design, the most important values are:
movement diameter
movement height
stem axis
rotor envelope
dial-side stack
date display position where applicable
movement securing method
The movement diameter controls internal case geometry, movement holder design, radial clearance, and movement seating.
The movement height controls axial clearance, case thickness, caseback depth, rotor clearance, dial height, hand stack planning, and retention strategy.
The SW300-1 should therefore be treated as a slim automatic case-design input, not merely as a specification sheet.
Why the SW300-1 Matters for Case Design
The SW300-1 matters because it gives designers a modern slim automatic movement option in the 25.60 mm diameter class.
It supports thinner case architecture than thicker standard automatic movements such as SW200-1 or ETA 2824-2, but it still carries automatic movement constraints.
A slim automatic case still needs:
rotor clearance
caseback depth
dial-side stack control
hand-to-crystal clearance
crown and stem alignment
movement securing
gasket compression
case stiffness
tolerance control
manufacturing validation
The SW300-1 should not be treated as a shortcut to thinness.
It is a slimmer movement foundation that must still be translated into complete case architecture.
Supporting pages:
→ Movement-Led Watch Case Design
→ Watch Movement Dimensions Explained
→ Watch Case Design System
Relationship to ETA 2892-A2
The SW300-1 is commonly described as Sellita’s alternative to the ETA 2892-A2. Grail Watch Reference describes the SW300-1 as a thin automatic movement designed as an alternative to ETA 2892A2, and Caliber Corner also identifies the SW300/SW300-1 family as related to the ETA 2892-A2 architecture.
This relationship matters for case design because both movements sit in the same slim 25.60 mm automatic design category.
From a case architecture perspective, both movements raise similar design questions:
slim axial stack control
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 the movements should be treated as automatically identical in every detail.
The final case must always be checked against the exact movement, hand height, dial system, date variant, and manufacturer data being used.
Supporting pages:
→ ETA 2892-A2 Dimensions & Technical Data for Watch Case Design
→ ETA 2892-A2 Case Design Guide
→ Movement Height vs Case Thickness
Movement Diameter and Internal Case Geometry
The SW300-1 has a 25.60 mm case-fitting diameter.
This value does not mean the internal case cavity should simply be cut to 25.60 mm.
The case must also account for:
radial clearance
movement holder geometry
movement seating
anti-rotation control
case machining tolerance
surface finishing allowance
assembly behaviour
service access
case wall thickness
The movement must be located accurately without being forced into the case.
A correct SW300-1 case defines the movement position through controlled internal geometry, not through loose placement inside a generic cavity.
Supporting pages:
→ Internal Case Geometry & Movement Cavity Sizing
→ Radial Clearance
→ Movement to Case Fit
Movement Height and Thin-Case Planning
The SW300-1 is commonly listed at approximately 3.60 mm high. That places it in the same slim automatic height class as the ETA 2892-A2 and makes it significantly thinner than standard 4.60 mm-class automatic movements such as SW200-1 or ETA 2824-2.
That height is useful, but it is not the final case thickness.
The complete axial stack must still include:
rotor clearance
caseback internal depth
caseback thickness
caseback gasket compression
movement seating height
dial thickness
dial seat height
hand stack height
hand-to-crystal clearance
crystal thickness
crystal retention geometry
bezel or midcase structure
A case designed only around the 3.60 mm movement height will usually be incomplete.
The SW300-1 gives the designer a thinner automatic foundation, but the case still has to protect the movement, rotor, dial-side stack, and sealing system.
Supporting pages:
→ Movement Height vs Case Thickness
→ Axial Clearance
→ Hand Stack Height and Clearance Requirements
Rotor Clearance and Caseback Planning
The SW300-1 is an automatic movement, so rotor clearance remains a core case design requirement.
A slim movement does not remove the need for caseback depth.
The caseback must allow for:
rotor movement
rotor endshake
movement manufacturing variation
caseback tolerance
gasket compression
shock behaviour
assembly variation
surface finishing effects
Rotor interference can cause scraping, poor winding performance, noise, drag, visible wear, and movement damage.
The caseback is therefore not simply a rear cover.
It is part of the movement-protection and axial-clearance system.
Supporting pages:
→ Rotor Clearance Requirements for Automatic Movements
→ Watch Caseback Design and Fit
→ Water Resistance Engineering in Watch Cases
Stem Height and Crown Alignment
The stem height of the SW300-1 defines where the crown and stem axis must pass through the case.
The crown tube position should not be chosen from external styling first.
Incorrect crown and stem alignment can cause:
stem bending
rough winding feel
poor setting action
keyless works stress
case tube misalignment
crown sealing problems
premature wear
movement shift during use
Because SW300-1 cases are often designed to be thinner, crown alignment errors can become more difficult to hide.
The case must define the crown tube position from the movement datum.
Supporting pages:
→ Crown and Stem Alignment in Watch Cases
→ Crown Tube Positioning & Geometry
→ Crown Tube Installation & Tolerances
Dial, Hands, Date, and Crystal Stack
The SW300-1 may be used in date or no-date configurations depending on variant and watch design.
The dial-side stack must account for:
dial thickness
dial seating height
date window alignment where applicable
dial support
hand stack height
hand-to-crystal clearance
rehaut height
crystal internal clearance
crystal retention geometry
The case cannot be designed only from the movement body.
The dial, hands, date system, rehaut, and crystal must be resolved as part of the complete case stack.
If the dial-side stack is uncontrolled, the hands may contact the crystal, the date window may misalign, or the total case height may increase unnecessarily.
Supporting pages:
→ Dial Seat Geometry
→ Hand Stack Height and Clearance Requirements
→ Dial to Crystal Clearance
Movement Securing and Retention
The SW300-1 must be retained securely inside the case.
The securing system must prevent:
radial movement
axial lift
rotation
dial shift
stem loading
caseback pressure transfer
movement stress during assembly
Movement securing may involve a movement holder, spacer ring, clamps, screws, retaining ledges, caseback control, or a combined system.
The movement should not be allowed to float radially.
It should not be compressed accidentally between the dial side and caseback.
Retention must be designed deliberately as part of the internal case architecture.
Supporting pages:
→ Movement Securing Methods
→ Axial Retention & Movement Stack Control
→ Internal Case Geometry & Movement Cavity Sizing
SW300-1 Compared With SW200-1
The SW300-1 and SW200-1 are both Sellita automatic movements, but they are not the same case-design problem.
The SW200-1 belongs to the thicker standard automatic architecture class. The SW300-1 belongs to the slimmer automatic architecture class.
Both use the same broad 25.60 mm movement diameter class, but the SW300-1’s 3.60 mm height changes the vertical case problem compared with the SW200-1’s thicker architecture.
This affects:
case thickness potential
caseback depth
rotor clearance planning
dial-side stack freedom
crown alignment sensitivity
thin-case rigidity
sealing geometry
manufacturing tolerance
A SW300-1 case should not be treated as a SW200-1 case with height removed.
It should be designed as a slim automatic case architecture from the beginning.
Supporting pages:
→ SW200-1 Dimensions & Technical Data
→ SW200-1 Case Design Guide
→ SW200-1 Case Design Constraints
What the Manufacturer Data Does Not Tell You
Manufacturer movement data gives essential dimensions, but it does not design the watch case.
The datasheet does not fully define:
how much radial clearance to use
how the movement should be retained
how much rotor clearance is safe
how the caseback should be shaped
how gasket compression affects total height
how the dial stack should be controlled
how machining tolerance affects fit
how finishing changes dimensions
how the crown tube should be integrated into the case
how the case should be validated before production
The published SW300-1 dimensions are the starting point.
They are not the complete case architecture.
Supporting pages:
→ Watch Movement Dimensions Explained
→ Watch Case Design Fundamentals
→ Watch Case Design System
Common SW300-1 Case Design Mistakes
Common mistakes include:
treating 25.60 mm as the finished case cavity size
treating 3.60 mm as the final case-thickness answer
forgetting rotor clearance
placing the crown visually instead of from the stem axis
allowing the movement to float radially
using uncontrolled caseback compression as retention
ignoring dial and hand clearance
misaligning the date window where used
underestimating gasket compression
failing to plan thin-case rigidity
assuming SW300-1 and ETA 2892-A2 cases are automatically interchangeable without checking details
Most of these failures come from treating the movement as a component to insert into a case rather than the foundation that defines the case.
Supporting pages:
→ Why Most Watch Case Designs Fail
→ Failure Cascade Analysis
→ Design Validation Checklist
Case Design Implications
For SW300-1 case design, the case should be planned around:
25.60 mm case-fitting diameter
3.60 mm movement height
controlled radial clearance
automatic rotor clearance
caseback depth
stem height and crown tube position
dial-side stack height
date display alignment where applicable
hand-to-crystal clearance
movement securing
gasket compression
thin-case rigidity
manufacturing tolerances
assembly sequence
The SW300-1 is especially useful where a slim automatic movement architecture is required.
But the movement only provides the foundation.
The case architecture determines whether that foundation becomes functional, manufacturable, and reliable.
HorologyCAD Design Position
Within the HorologyCAD system, the Sellita SW300-1 is best understood as a slim automatic reference movement.
It is useful for explaining:
modern Sellita thin automatic case architecture
relationship to ETA 2892-A2-style case design
radial and axial clearance planning
automatic rotor clearance
caseback depth
crown alignment in thinner cases
movement holder design
date and dial-side stack control
manufacturable slim automatic case geometry
The SW300-1 should not be approached as a generic automatic movement.
It should be approached as a slim automatic reference calibre that defines a specific movement-led case design problem.
A correct SW300-1 case begins with the movement dimensions, but it must continue through clearance planning, stem alignment, rotor protection, movement retention, sealing, tolerance control, and validation.
For the broader framework, return to the HorologyCAD homepage.