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Movement comparison

7S26 vs NH35

no day; same diameter; 0.42 mm taller; different hand holes. Can NH35 replace 7S26? Only with changes to the watch or parts. Some fit figures are still unpublished, so this verdict is not confirmed.

Sources checked · How we source numbers
Movements to scale: Seiko 7S26, TMI NH35Dial side and side section at one scale, hand holes enlarged 8:1. A Seiko 7S26: Ø 27.4, H 4.9, date 3H, crown —. B TMI NH35: Ø 27.4, H 5.32, date 3H, crown 3H (vs A: Ø 0 H +0.42 mm).A Ø 27.4B Ø 27.4A 4.9B 5.32SIDE · HEIGHTS ON ONE BASELINEHAND HOLES · 8:1A hour 1.5 · minute 0.9 · second 0.21B hour 1.5 · minute 0.88 · second 0.198A Seiko 7S26Ø 27.4 · H 4.9 · date 3H · crown —B TMI NH35Ø 27.4 · H 5.32 · date 3H · crown 3Hvs A: Ø 0 H +0.42 mm
7S26 vs NH35 to one scaleDrawing from data, not a photo · mm

Published figures

Differences are highlighted. Each number links to its source; an empty field says what is missing.

7S26 vs NH35 specification comparison
FigureASeiko 7S26BTMI NH35
Diameter27.4 mm1seller listing27.4 mm3
Casing diameterdiffers27 mm1seller listing29.36 mm3
Size in lignesone side onlynot published12‴4
Heightdiffers4.9 mm1seller listing5.32 mm3
Jewelsdiffers216244
Beat rate21,600 bph621,600 bph4
Power reserve41 h641 h5
Accuracy (maker)one side onlynot in the documents we read−20 to +40 s/day5
Lift angleone side onlynot in the documents we read53°5
Hands and functionsdiffershours, minutes, centre seconds, date, day6 · date, day2hours, minutes, centre seconds, date4
Hacking secondsone side onlynot published by SeikoYes4
Hand windingone side onlynot published by SeikoYes5
Date window3H2secondary source3H5 · 3H, 6H, 9H7
Do not set the date21:00–04:00621:00–04:008
Crownone side onlynot in the documents we read3H5 · 4H9
Hand holesdiffershour 1.5 · minute 0.9 · second 0.21 mm1seller listinghour 1.5 · minute 0.88 · second 0.198 mm7
Dial feetone side onlynot in the documents we read1:36, 7:337 · 1:36, 7:337
Dial centre holeone side onlynot published2.05 mm7

Can NH35 replace 7S26?

The direction matters: this checks a watch built for the first calibre with the second installed. Size alone does not prove that hands, dial, stem and case will fit.

Fits with changes· not confirmed
  • =diameterSame movement diameter: 27.4 mm.
  • ≠heightNH35 is 0.42 mm taller (5.32 mm vs 4.9 mm): check the room under the crystal and the case back; the hands sit higher.
  • ≠handsDifferent hand holes (minute 0.9 vs 0.88 mm): new hands.
  • ≠dateNH35 has no day wheel: a day-date dial would show an empty day window.
  • =dateDate window at 3H on both.

Not published, so not checked: crown position for 7S26; dial feet for 7S26.

Check the actual case, stem height and parts before ordering. Compare another pair.

Sources

Documents checked · Report a wrong number

  1. 1Esslinger & Co. — Genuine Seiko 3 Hand Automatic Watch Movement 7S26 (product page, movement marked 7S26C) · html · read
  2. 2Grail Watch — Grail Watch Reference: Seiko Cal. 7S26 · html · read
  3. 3Time Module Ltd. — Watch Movement Specification and Drawing - Standard Mechanical Movement NH35A · pdf · read
  4. 4Time Module Ltd. — Product Line-Up - Mechanical (NH0&NH3); NH34/NH35/NH36 product blocks · html · read
  5. 5Time Module Ltd. — Technical Guide & Parts Catalogue, Cal.NH3 Series (NH34A/35A/36A/37A/38A/39A) - Automatic Mechanical · pdf · read
  6. 6Seiko Watch Corporation — Instructions: Seiko Automatic Diver's Watch Cal. 4R15/4R16/4R35/4R36/7S26/7S35/7S36 (English) · pdf · read
  7. 7Time Module Ltd. — Watch Movement Specification and Drawing - NH35A (drawing pages read: Appearance-1, Hand Fitting, Hand Setting Stem, Dial-1, Dial-2, Hands) · pdf · read
  8. 8Time Module Ltd. — Operation Manual, Cal.NH3 Series (NH34A/35A/36A/37A/38A/39A) · pdf · read
  9. 9Lucius Atelier (seller) — Seiko Mod Dial Compatibility Guide: NH34, NH35, NH36 (blog article) · html · read