Definition
Sellita SW200-1 dimensions define the movement diameter, height, stem position, clearance requirements, hand stack, caseback depth, and engineering parameters needed for movement-led watch case design.
The SW200-1 is not only a movement selected for timekeeping. In case design, it becomes the fixed internal reference geometry that controls the movement cavity, crown position, axial stack, dial interface, hand clearance, caseback position, and movement retention system.
These values are not passive reference numbers.
In movement-led case design, they become fixed design constraints.
Why SW200-1 Dimensions Matter
A watch case designed around the SW200-1 must begin from verified movement geometry.
The movement defines:
- Internal case geometry
- Movement cavity diameter
- Crown and stem alignment
- Axial stack structure
- Dial seat position
- Hand clearance envelope
- Caseback and rotor clearance
- Movement retention requirements
Incorrect dimensional assumptions can result in:
- Stem and crown misalignment
- Dial or hand clearance failure
- Caseback interference
- Rotor obstruction
- Poor movement retention
- Assembly incompatibility
- Functional failure under operation
A case can look correct externally and still fail if the internal architecture is not derived from the movement.
Manufacturer Technical Basis
The SW200-1 technical documentation provides the dimensional basis for case design. Sellita documentation identifies the SW200-1 as an 11½ ligne automatic calibre and gives the technical drawing basis for case fitting, crown/stem position, and movement interfaces.
The common published headline dimensions are approximately 25.60 mm case-fitting diameter and 4.60 mm movement height.
These values should always be checked against the latest official Sellita technical documentation before being used for manufacturing or final CAD release.
Manufacturer data is the starting point, not the finished case solution.
The technical documentation does not provide a complete watch case architecture. It does not define the designer’s final radial clearance strategy, axial stack allowance, crown tube installation method, gasket compression, caseback structure, movement holder design, machining tolerance strategy, or external case styling.
That is the role of movement-led case design.
Core SW200-1 Dimensions
Movement Diameter
Approximate case-fitting diameter: 25.60 mm.
This dimension controls:
- Minimum internal case cavity size
- Movement holder geometry
- Radial clearance strategy
- Internal shoulder and support geometry
- Assembly behaviour during casing
The case cavity should not simply copy the movement diameter. It must include controlled clearance, machining allowance, tolerance behaviour, and a defined method of movement retention.
Radial behaviour is resolved through Radial Clearance Between Movement and Case.
Movement Height
Approximate movement height: 4.60 mm.
This dimension controls:
- Axial stack baseline
- Minimum internal case depth
- Dial-side positioning
- Caseback position
- Rotor clearance
- Total case thickness
Movement height is not the same as final case thickness. The final vertical architecture also depends on dial thickness, hand stack height, crystal clearance, caseback clearance, rotor space, gasket geometry, and retention method.
Vertical behaviour is governed by Movement Height vs Case Thickness and Axial Clearance.
Stem Height
Approximate stem height: 1.80 mm from the movement support plane / casing reference, depending on the technical drawing convention used.
Stem height controls:
- Crown tube vertical position
- Case wall bore location
- Crown seat geometry
- Stem alignment
- Crown operation under load
This is one of the most important SW200-1 case design constraints.
The crown tube cannot be positioned from external styling alone. It must be derived from the movement stem axis first, then integrated into the case wall and crown design.
Alignment must be resolved through Stem Height to Crown Tube Position Relationship and Crown and Stem Alignment.
Stem Position
The SW200-1 stem position is fixed relative to the movement centreline.
This controls:
- Crown placement
- Case side geometry
- Crown tube bore location
- External crown symmetry
- Relationship between movement centre, dial centre, and case centre
The stem axis is not adjustable. If the case tube is misplaced, the design must be corrected at the case level, not by forcing the stem into alignment.
Dial Interface
Dial Diameter
Dial diameter is design-dependent. In many SW200-1 case designs it may sit around 28.0–29.0 mm, but the final value depends on the dial seat, rehaut, case opening, and visual architecture.
Dial diameter controls:
- Dial seat geometry
- Rehaut position
- Chapter ring clearance
- Visual proportions
- Case opening size
The dial is not defined by the movement diameter alone. It must be coordinated with the movement location, dial feet, hand stack, rehaut, and crystal opening.
Dial Feet Position
Dial feet position is movement-specific.
This controls:
- Dial attachment
- Dial rotational alignment
- Date window alignment where applicable
- Relationship between dial graphics and crown/stem orientation
Dial feet must match the movement. A dial that appears dimensionally suitable can still be unusable if the feet do not align with the SW200-1 dial mounting positions.
Hand Stack Parameters
The hand stack defines the vertical clearance required above the dial.
It includes:
- Hour hand clearance above the dial
- Minute hand clearance above the hour hand
- Seconds hand clearance above the minute hand
- Clearance below the crystal
- Allowance for hand flex, dial tolerance, and assembly variation
Hand stack behaviour controls:
- Dial height
- Crystal underside clearance
- Rehaut depth
- Total case thickness
- Risk of hand collision
A case can have correct movement diameter and correct crown alignment but still fail if the hands collide with the dial, each other, or the crystal.
Hand stack behaviour must be validated through Axial Clearance and Hand Stack Height and Clearance Requirements.
Crown and Stem Interface
The SW200-1 crown and stem interface affects both function and sealing.
The stem controls:
- Crown engagement
- Keyless works operation
- Crown pull positions
- Torque transmission
- Tube bore alignment
- Seal compatibility
The crown system must allow:
- Full stem engagement
- Smooth crown operation
- No lateral stem loading
- No axial preload
- Stable operation across winding, date correction, and time setting
The case tube must support sealing and crown operation without forcing the stem away from its natural axis.
Movement Mounting and Retention
The SW200-1 must be retained without distorting the movement or allowing uncontrolled movement inside the case.
Movement mounting geometry controls:
- Clamp engagement
- Movement holder design
- Spacer ring geometry
- Axial retention
- Service access
- Shock behaviour
The retention system must prevent movement shift while avoiding excess preload.
A movement that is too loosely retained can move under shock or crown operation. A movement that is over-constrained can suffer from assembly stress, alignment problems, or serviceability issues.
Retention behaviour must align with Movement Securing Methods and Axial Retention and Movement Stack Control.
Tolerance Considerations
Nominal movement dimensions are not sufficient for case design.
Critical tolerance-sensitive areas include:
- Movement diameter
- Movement height
- Stem height
- Dial position
- Hand height
- Caseback clearance
- Crown tube bore position
- Movement holder fit
The case must account for:
- Movement manufacturing variation
- Case machining tolerance
- Dial thickness variation
- Hand fitting variation
- Gasket compression
- Assembly sequence
- Finishing and coating allowance
The goal is not to make the case as tight as possible.
The goal is to make the movement fit repeatably, assemble correctly, and remain stable in use.
Clearance Requirements
Clearance must be defined deliberately.
Typical controlled clearance zones include:
- Radial clearance between movement and case
- Axial clearance above and below the movement
- Dial-to-crystal clearance
- Rotor-to-caseback clearance
- Crown tube-to-stem alignment allowance
Very small clearances such as 0.02–0.05 mm may be relevant in specific controlled interfaces, but they should not be treated as universal values for the entire case design.
Actual clearance depends on machining method, tolerance stack, finishing, assembly method, movement holder design, and the specific interface being controlled.
Clearance must:
- Allow reliable assembly
- Avoid binding
- Prevent uncontrolled movement
- Survive tolerance variation
- Preserve function after casing
Radial and axial clearance should be treated as separate engineering problems, not one general “fit” allowance.
Interaction with Watch Case Design
SW200-1 dimensions directly define the internal case system.
They control:
- Internal case geometry
- Movement holder size
- Dial seat position
- Crown tube location
- Hand clearance envelope
- Caseback depth
- Rotor clearance
- Retention strategy
- Serviceability
The external case design must respect these internal constraints.
Lugs, bezel form, case profile, crown guards, and visual styling can vary, but the internal movement-fit architecture must remain controlled around the SW200-1.
Why Raw Movement Dimensions Are Not Enough
A movement datasheet gives the dimensions of the movement.
It does not give the full case architecture required to house it correctly.
Raw SW200-1 dimensions do not define:
- Final case cavity geometry
- Movement holder design
- Radial clearance strategy
- Axial stack allowance
- Crown tube installation
- Caseback sealing structure
- Rotor clearance
- Dial and rehaut architecture
- Crystal clearance
- Machining process tolerance
- Assembly validation
This is the gap between movement data and manufacturable watch case design.
HorologyCAD treats the movement data as the fixed technical basis, then translates that data into case architecture decisions.
Movement-Specific Case Architecture
Designing a case around the SW200-1 requires more than placing a 25.60 mm movement into a larger circular cavity.
The case must control radial clearance, axial stack height, stem alignment, crown tube position, dial seating, hand clearance, caseback space, and movement retention as one connected system.
HorologyCAD is being developed around movement-specific, lug-agnostic case architecture systems. The purpose is to provide a manufacturable internal case foundation that can be adapted into different external case styles without redesigning the movement fit from zero each time.
The SW200-1 is one of the primary reference movements for this system.
Common SW200-1 Case Design Failures
Common failures include:
- Internal cavity sized from nominal movement diameter only
- Crown tube positioned from exterior case design rather than stem height
- Insufficient rotor clearance under the caseback
- Dial height not coordinated with hand stack
- Crystal underside too close to the seconds hand
- Movement holder too loose or over-constrained
- Caseback used to force axial retention without proper stack control
- Stem forced into alignment during assembly
- Tolerance stack ignored until prototyping
Most failures do not come from misunderstanding one dimension.
They come from failing to treat all dimensions as one connected system.
System Context
This page forms the dimensional foundation for SW200-1 movement-led case design.
It supports downstream decisions involving:
- Movement-specific case design
- Internal case geometry
- Radial clearance
- Axial clearance
- Crown and stem alignment
- Dial and hand stack control
- Movement retention
- Caseback and sealing design
- Manufacturability
The SW200-1 defines the internal reference system.
The case must be designed around it.
Final Statement
The SW200-1 defines the fundamental dimensional constraints of the watch case.
Accurate interpretation of these values is required to:
- Maintain alignment across interfaces
- Control radial and axial clearance
- Position the crown tube correctly
- Protect hand and rotor clearance
- Ensure manufacturability and assembly
- Deliver reliable long-term performance
All case design must be derived from verified movement geometry.
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