Definition
This page defines the critical dimensions and engineering parameters of the NH35 / NH36 movement family required for movement-led watch case design.
The NH35 and NH36 are not only automatic movements selected for timekeeping. In case design, they become fixed internal reference systems that control the movement cavity, spacer relationship, crown position, axial stack, dial interface, hand clearance, caseback position, rotor clearance, and movement retention system.
These values are not passive reference numbers.
In movement-led case design, they become fixed design constraints.
Why NH35 / NH36 Dimensions Matter
A watch case designed around the NH35 or NH36 must begin from verified movement geometry.
The movement defines:
- Internal case geometry
- Movement cavity diameter
- Dial holding spacer relationship
- 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
- Rotor or caseback interference
- Poor movement retention
- Incorrect spacer fit
- Assembly incompatibility
- Unnecessary case thickness
- Functional failure under operation
The NH35 / NH36 family is widely used in modding, independent watch projects, and entry-level automatic case design. That popularity can make the movement seem simple to integrate, but case compatibility is not defined by popularity.
A case can accept an NH35 visually and still fail if the internal movement-fit architecture is not controlled.
Manufacturer Technical Basis
The NH3 Series technical documentation provides the dimensional basis for case design. Technical guides for the NH35A / NH36A family identify an outside diameter of 27.40 mm, a casing diameter of 29.36 mm with dial holding spacer, and a total height of 5.32 mm.
The NH3 Series technical guide also identifies the family as automatic mechanical movements with 21,600 vibrations per hour, manual winding, stop-second device, and date or day-date functions depending on the calibre variant. NH35 uses a date calendar, while NH36 includes day and date functionality.
These values should always be checked against the latest official 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 NH35 / NH36 Dimensions
Movement Diameter
Approximate outside diameter: 27.40 mm.
Approximate casing diameter with dial holding spacer: 29.36 mm.
This dimension controls:
- Minimum internal case cavity size
- Dial holding spacer relationship
- Movement holder geometry
- Radial clearance strategy
- Internal shoulder and support geometry
- Assembly behaviour during casing
The NH35 / NH36 cannot be treated only as a bare movement diameter. The casing diameter with spacer is often the more important practical case-design reference because it defines how the movement is supported and located in many case systems.
The case cavity should not simply copy either nominal 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 total height: 5.32 mm.
This dimension controls:
- Axial stack baseline
- Minimum internal case depth
- Dial-side positioning
- Caseback position
- Rotor clearance
- Total case thickness
The NH35 / NH36 is thicker than slimmer automatic movements such as the Miyota 9015. That does not make it unsuitable for case design, but it does mean that vertical stack planning becomes especially important.
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, spacer/holder geometry, and retention method.
Vertical behaviour is governed by Movement Height vs Case Thickness and Axial Clearance.
Stem Height
Stem height defines the vertical position of the crown and stem interface relative to the movement’s casing reference.
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 NH35 / NH36 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 NH35 / NH36 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.
NH35 vs NH36 Calendar Interface
The NH35 and NH36 are closely related, but their calendar interfaces are not identical.
The NH35 uses a date calendar.
The NH36 uses day and date functionality.
This affects case and dial design because the dial, date window, day/date display, and crown setting behaviour must match the selected movement variant.
The case designer must account for:
- Date window position
- Day/date window requirements where applicable
- Dial print and aperture alignment
- Crown setting positions
- Dial-side clearance
- Movement variant compatibility
A case architecture that fits the movement mechanically may still fail as a complete watch if the dial and calendar interface are not coordinated.
Dial Interface
Dial Diameter
Dial diameter is design-dependent. In many NH35 / NH36 projects, the dial is selected around common modding or microbrand formats, but the final value depends on the dial seat, rehaut, case opening, date/day-date display, and visual architecture.
Dial diameter controls:
- Dial seat geometry
- Rehaut position
- Chapter ring clearance
- Date or day/date window relationship
- 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, calendar display, and crystal opening.
Dial Holding Spacer
The NH35 / NH36 family is commonly considered with its dial holding spacer relationship. The technical guide gives the casing diameter as 29.36 mm with dial holding spacer, making the spacer relationship an important practical design condition.
The spacer affects:
- Movement support
- Movement seating
- Dial-side relationship
- Radial fit
- Assembly behaviour
- Retention strategy
The case should not assume that the bare movement diameter alone defines fit. The spacer and holder relationship can become the dominant interface between the movement and the case.
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 length, hand flex, dial tolerance, and assembly variation
The NH3 Series guide gives hand attachment and setting procedures, including caution around correct hand installation and movement handling during hand fitting.
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, the rehaut, or the crystal.
Hand stack behaviour must be validated through Axial Clearance and Hand Stack Height and Clearance Requirements.
Crown and Stem Interface
The NH35 / NH36 crown and stem interface affects both function and sealing.
The stem controls:
- Crown engagement
- Keyless works operation
- Crown pull positions
- Date or day/date correction
- 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, calendar 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 NH35 / NH36 must be retained without distorting the movement or allowing uncontrolled movement inside the case.
Movement mounting geometry controls:
- Holder or spacer design
- Clamp or screw compatibility
- Movement seating
- 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
- Casing diameter with spacer
- Movement height
- Stem height
- Dial position
- Hand height
- Rotor clearance
- Caseback clearance
- Crown tube bore position
- Movement holder or spacer fit
The case must account for:
- Movement manufacturing variation
- Case machining tolerance
- Dial thickness variation
- Hand fitting variation
- Spacer/holder 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/spacer and case
- Axial clearance above and below the movement
- Dial-to-crystal clearance
- Rotor-to-caseback clearance
- Crown tube-to-stem alignment allowance
- Holder or spacer clearance
Clearance should not be treated as one general allowance across the entire case.
Actual clearance depends on machining method, tolerance stack, finishing, assembly method, movement holder design, spacer relationship, 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
NH35 / NH36 dimensions directly define the internal case system.
They control:
- Internal case geometry
- Movement holder or spacer size
- Dial seat position
- Crown tube location
- Hand clearance envelope
- Calendar display alignment
- 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 NH35 / NH36.
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 NH35 / NH36 dimensions do not define:
- Final case cavity geometry
- Movement holder or spacer design
- Radial clearance strategy
- Axial stack allowance
- Crown tube installation
- Caseback sealing structure
- Rotor clearance
- Dial and rehaut architecture
- Calendar display alignment
- 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 NH35 / NH36 requires more than placing a 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, rotor clearance, calendar display alignment, and movement retention as one connected system.
The NH35 / NH36 family is popular partly because of its availability and compatibility with many modding ecosystems, but compatibility does not remove the need for proper case architecture.
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 NH35 / NH36 is one of the primary reference movement families for this system.
Common NH35 / NH36 Case Design Failures
Common failures include:
- Internal cavity sized from nominal movement diameter only
- Dial holding spacer relationship ignored
- Crown tube positioned from exterior case design rather than stem height
- NH35 and NH36 calendar interfaces treated as identical
- Insufficient rotor clearance under the caseback
- Dial height not coordinated with hand stack
- Crystal underside too close to the seconds hand
- Movement holder or spacer 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 NH35 / NH36 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
- Calendar interface alignment
- Movement retention
- Caseback and sealing design
- Manufacturability
The NH35 / NH36 defines the internal reference system.
The case must be designed around it.
Final Statement
The NH35 / NH36 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
- Coordinate the spacer and calendar interface
- Ensure manufacturability and assembly
- Deliver reliable long-term performance
All case design must be derived from verified movement geometry.
Return to Homepage
Return to HorologyCAD Homepage.