Documented starting points
TMI's NH35A drawing specifies a 27.40 mm movement diameter, 29.36 mm with its dial-holding spacer, and 5.32 mm height.1 Its technical guide describes a three-hand, date-only calibre; the guide includes NH34–NH39 but does not certify interchange with Seiko retail-watch parts.2
Seiko identifies both the SRPD55 and SRPD51 as 5 Sports models in its SKX series. Each official product page specifies a 4R36 day/date movement, 42.5 mm case diameter, 46.0 mm lug-to-lug length, 22 mm distance between lugs and 10 bar water resistance.34 Those are complete-watch specifications, not bezel-seat, crystal-seat or movement-holder drawings.
Check each part against the relevant drawing
| Part | Documented fact | Still needed for a fit decision |
|---|---|---|
| Movement and case | NH35A: Ø27.40 mm, or Ø29.36 mm with dial spacer; 5.32 mm high. SRPD55/51: stock 4R36. | Movement holder, case bore, stem height and alignment, crown engagement, caseback and rotor clearance. |
| Dial and date | NH35 is date-only; stock SRPD55/51 use a day/date 4R36. | Dial feet, dial diameter, window position and whether a day window would expose empty space. |
| Hands | NH35A hand bores in the TMI drawing: hour Ø1.50, minute Ø0.88, seconds Ø0.198 mm. | Exact hand tolerances, mounting height, sweep diameter, dial and crystal clearance. |
| Strap | Seiko publishes 22 mm between the lugs for SRPD55 and SRPD51. | Length, thickness, end-link shape and spring bars for the chosen strap; 22 mm does not establish fitted-end-link fit. |
| Bezel and crystal | The SRPD product pages name a unidirectional bezel and Hardlex crystal. | Seat diameters, heights, gasket profiles and retention method on the exact watch and replacement part. |
The hand figures above are bores transcribed from TMI's NH35A “Hands” drawing, with its drawing units converted to millimetres.1 Always use the original drawing and part revision for tolerances. A nominal hole size does not prove that a long hand clears the crystal.
Why SRPD “SKX series” does not mean SKX007 fit
“SKX series” is Seiko's collection label on the SRPD55 and SRPD51 pages.3 The SKX007 is a separate watch reference. We have no manufacturer fit drawing that maps its bezel, crystal, caseback or crown interface onto an SRPD. For those parts the current answer is unknown, even when published outer case measurements look similar.
Check your own reference before using the checklist: the SRPD79, SRPD59 and SRPD65 each have separate model pages. A figure on one SRPD page is not automatically a measurement of another variant.
A useful order before assembly
- Write down the exact watch reference and the movement code from the actual parts. Do not buy by “SKX style” alone.
- For each part, record the mating dimension and its source: maker drawing, reliable part drawing or direct measurement. Mark a blank as unknown rather than assuming a fit.
- Check the date/day layout, dial feet, stem-to-crown alignment and hand stack as a complete system before pressing hands or cutting a stem.
- Dry-fit the case components; after any seal or case change, re-test water resistance before water exposure.
The visual builder can preview a design, but its layered artwork is not a dimensional approval. Start the physical checklist from the NH35 source drawings.