Which watches does the Seiko 5 donor name cover?

Seiko 5 names a family with different references and case designs. This guide uses SRPD51 and SRPK89 as documented examples. Check the full reference of your own watch before planning parts.

Do all Seiko 5 watches share one movement and case size?

No family-wide specification should be inferred. Seiko lists 4R36 for SRPD51 and SRPK89, but their case diameters are 42.5 mm and 37.4 mm respectively. Movement and case size therefore depend on the individual reference.

Are the linked MedoMods watches original Seiko 5 models?

MedoMods builds and sells finished mods with their own specifications. The links show style alternatives and do not establish original Seiko 5 donor provenance.

Seiko 5 Mod: choose a donor for diver, field and dress styles

Seiko 5 is a family rather than a single donor watch. Start with the full reference: Seiko lists 4R36 for both Seiko 5 Sports SRPD51 and SRPK89, yet their case dimensions differ. Choose the case proportions and dial style for your build, then check the actual parts. MedoMods builds and sells finished mods with their own specifications.

Specifications

Reference: Check the full Seiko 5 model reference before selecting parts.
Movement examples: SRPD51 and SRPK89: Seiko 4R36, automatic with manual winding, a stop-seconds function and a day/date display.
Case diameter examples: SRPD51: 42.5 mm. SRPK89: 37.4 mm. These dimensions apply only to the named references.
Crystal examples: SRPD51: Hardlex. SRPK89: curved Hardlex.
Water resistance examples: Seiko specifies 10 bar for original SRPD51 and SRPK89 watches; this is not a rating for a modified watch.

Manufacturer sources

Planning a Seiko 5 mod

Compare the full reference rather than treating all Seiko 5 watches as one parts platform.
Choose case proportions and display functions before the dial design.
Use reference-specific measurements for the crystal, bezel, dial and hands.

Ideas for a build

Field style: Arabic numerals and a textile strap, after checking dial and strap fit.
Dress style: a sunburst dial and slim hands, matched to the case and movement.

Two Seiko 5 Sports references, different proportions

SRPD51 has a 42.5 mm case diameter and 22 mm lug width; SRPK89 has a 37.4 mm case diameter and 18 mm lug width. Seiko specifies 4R36 for both. A shared calibre does not make the cases, crystals, bezels or bracelets interchangeable.

Plan the donor and the parts together

Read the exact reference and fitted calibre, then compare component dimensions. For a day/date design, check the dial openings and movement layout; for a field or dress look, check dial diameter and hand clearances. A Seiko 5 family label does not establish part compatibility.

Finished MedoMods watches in related styles

Explore DATE and OYST for finished MedoMods designs. Compare each model’s movement, measurements and functions. The linked collections offer style alternatives; they do not claim an original Seiko 5 donor was used.

Donor models Check dial design and dimensions

Donor watch questions

Which watches does the Seiko 5 donor name cover?: Seiko 5 names a family with different references and case designs. This guide uses SRPD51 and SRPK89 as documented examples. Check the full reference of your own watch before planning parts.
Do all Seiko 5 watches share one movement and case size?: No family-wide specification should be inferred. Seiko lists 4R36 for SRPD51 and SRPK89, but their case diameters are 42.5 mm and 37.4 mm respectively. Movement and case size therefore depend on the individual reference.
Are the linked MedoMods watches original Seiko 5 models?: MedoMods builds and sells finished mods with their own specifications. The links show style alternatives and do not establish original Seiko 5 donor provenance.