Seiko NH3x / NH7x Movement Family — Reference

Static reference page. Every dimension below is cited to either Time Module (TMI, the official manufacturer) or to Caliber Corner / DIY Watch Club's published transcription of TMI spec sheets. Verified 2026-05-11. Re-verify the manufacturer source if you're about to order based on these numbers — vendors sometimes publish their own (occasionally drift-prone) numbers.

What this family is

Time Module Inc. (TMI) is the wholesale parts arm of Seiko / Seiko Instruments Inc. (SII). They manufacture the NH-series mechanical movements and sell them unbranded for use in non-Seiko watches. The same movements appear in Seiko-branded watches under the 4R-series naming (e.g. NH35 ↔ 4R35, NH36 ↔ 4R36, NH38 ↔ 4R38, NH34 ↔ 4R34). The 4R variants are factory-regulated to a tighter spec; the NH variants are unregulated. Mechanically and dimensionally they are identical.

The family splits into two sub-series:

• NH3 series (NH34, NH35, NH36, NH38) — solid-plate movements with a 29.36mm dial-holding spacer ring. These are what most modder cases are built around. Casing diameter 29.36mm.
• NH7 series (NH70, NH71, NH72) — skeletonized movements with no dial spacer. Casing diameter 27mm. The dial side is meant to be visible through a skeleton dial or open-front design.

Both share the same 27.4mm bare movement diameter and the same 5.32mm bare height. They use the same dial-feet positions (3.0 / 3.8 / 9.0 / 9.8 o'clock). Hand pinion sizes are shared across the family except where a complication adds a post (NH34 GMT, NH36 day-date).

Shared specs (everything in the family unless noted)

Source: Caliber Corner caliber pages (linked per variant below) — each transcribes the official Time Module spec sheets. TMI's own spec sheet PDFs are linked at the bottom.

Hand pinion sizes (critical field for hands sourcing)

Hand-fit pinion sizes determine which hands you can buy. The pinion-to-tube fit must be exact — a tube ID that's too large will fall off, too small will not seat. Sources sometimes list these in TMI's native unit ("ligne/mm hundredths") rather than millimeters; the table below converts.

Note on rounding: TMI's official ligne notation is 150/89/21 (hundredths of a ligne). Caliber Corner publishes this as 1.5mm / 0.89mm / 0.21mm. Some modder community sources round to 1.5mm / 0.88mm / 0.20mm — close enough for casual reference but the published TMI numbers are 0.89 and 0.21. Always check the hands supplier's tube ID against the buy of the dial+hand kit, not against a rounded community number.

Note on Caliber Corner NH36 page: Caliber Corner's NH36 entry lists the minute pinion as 1.0mm — this is inconsistent with WR Accessories parts catalog (which lists the cannon pinion 0241-010 as shared between NH35 and NH36) and with the TMI family practice. Probable typo on Caliber Corner. Treat NH36 minute pinion as 0.89mm matching the family. Confirm before ordering if uncertain.

Dial feet

All NH3x and NH7x variants use the same dial-feet positions. A dial designed for one is mechanically compatible with another at the foot level (functional compatibility depends on whether the dial has a date aperture and the movement has a date wheel — see "Compatibility traps" below).

Most aftermarket modder dials ship with 4 dial feet at 3.0/3.8/9.0/9.8 and you "snip off the 2 legs accordingly" to fit your case's crown position. This is standard practice across DSWatch, NamokiMODS, Lucius Atelier, and the AliExpress/Taobao parts ecosystem.

Per-variant detail

NH34A — GMT (24-hour second time zone)

• Functions: 3 hands (H/M/S) + 24-hour GMT hand + date at 3 o'clock
• Crown positions: 0 winding / 1 GMT-hand setting + date / 2 time setting
• Notable feature: Adds a 24-hour hand on a separate central post (a "step" above the H/M stack); standard NH35 hands fit the H/M/S positions but you need a dedicated GMT hand for the 24-hour indicator
• Unique compatibility note: The extra central post means an NH34 has different cannon-pinion height than NH35; the additional GMT hand pinion adds height to the total stack. Caliber depth in the case must accommodate this.
• Released: ~2022 — newer than the rest of the family
• Source: Caliber Corner — Seiko NH34, DIY Watch Club NH34A specs

NH35A — 3-hander with date (the workhorse)

• Functions: 3 hands (H/M/S) + date at 3 o'clock (or 4 o'clock with rotated dial / different stem position)
• Crown positions: 0 winding / 1 date setting / 2 time setting
• Used in: the broadest mod-parts ecosystem; most aftermarket cases, dials, and hands are designed around this movement
• Notes: Hand-windable upgrade of the older NH25A
• Source: Caliber Corner — Seiko NH35A

NH36A — 3-hander with day + date

• Functions: 3 hands (H/M/S) + day display + date at 3 o'clock
• Crown positions: 0 winding / 1 day-and-date setting / 2 time setting
• Unique compatibility note: The day-date complication uses an additional wheel under the dial. Dials designed for NH36 have a different aperture cutout (day + date window combined or stacked). NH35-designed dials do NOT have the day cutout and will not work with an NH36 if you want the day to display.
• Source: Caliber Corner — Seiko NH36

NH38A — 3-hander, no date (open balance at 9)

• Functions: 3 hands (H/M/S); no date, no day
• Crown positions: 0 winding / 1 nothing / 2 time setting
• Notable feature: True no-date movement (date wheel is absent from the plate, not just hidden). The space normally occupied by the date wheel has an open balance wheel visible at the 9 o'clock position, which is a distinctive aesthetic feature for movements with sapphire casebacks.
• Unique compatibility note: A dial with a date aperture will expose the empty movement plate where the date wheel would be — there is no date wheel underneath to display anything through the aperture. Pairing a date-cutout dial with an NH38 leaves a visible hole that requires a plug at assembly. For a clean build, pair NH38 with a no-date dial.
• Source: Caliber Corner — Seiko (SII) NH38A

NH70A / NH71A / NH72A — Skeleton (no-date)

The NH7x sub-family is mechanically identical to the NH3x movements but the plates are skeletonized so the wheel train and balance are visible from the dial side. These are designed for open-front watches where the movement IS the dial.

• NH70A: Silver / steel-colored plates (the default)
• NH71A: Gilt / gold-colored plates
• NH72A: Ruthenium grey plates (PVD-like coating)
• Casing diameter: 27mm (smaller than NH3x's 29.36mm because there's no dial-holding spacer ring — the skeleton "dial" is the movement itself, retained by a different ring)
• Functions: 3 hands (H/M/S); no date
• Crown positions: 0 winding / 1 time setting (only two positions since no date)
• Compatibility: Dial feet positions are identical to NH3x per TMI; you can switch an NH35A in a 28.5mm-dial case to an NH70A but you must also swap the dial for a skeleton-compatible setup, since the NH7x doesn't use the dial-holding spacer ring.
• Source: Caliber Corner — Seiko NH70A, Caliber Corner — Seiko NH72

Compatibility traps (read before sourcing dials and hands)

These are the failure modes that have bitten Watch 001 sourcing. Each one is a coupling between the spec of one part and the spec of another — relaxing a rule on one side without re-checking the other side is the anti-pattern.

Date aperture ↔ date wheel

A dial with a date cutout (aperture) physically removes material at the 3 o'clock position. A movement with a date wheel rotates a numbered disc visible through that cutout. If you put a date-aperture dial on a no-date movement (NH38, NH70/71/72), the aperture exposes the empty movement plate — there's no disc rotating underneath. Plugging the aperture from behind doesn't restore the dial face; the cutout remains visible as a rectangular discontinuity in the dial finish. There is no clean fix for "no-date dial face but the dial has a date cutout" short of replacing the dial.

The flip side: putting a no-date dial on a date movement leaves a functional date wheel rotating under a sealed dial face — harmless, the date wheel just isn't visible. This is a clean configuration (and is how many no-date modders use NH35-based watches).

Day + date ↔ day-date dial

NH36 day-date has an additional day-of-week wheel. A dial designed for NH35 won't have the day cutout. A dial designed for NH36 has either a combined day-date window or a stacked layout. Mismatching here either hides the day display or leaves an empty cutout — same template-coupling issue as date apertures.

NH34 GMT hand ↔ GMT-compatible hand stack

The 24-hour GMT hand sits on its own central post. A standard NH35 hand set won't have a fourth hand for GMT, and the GMT hand cannot be a generic minute or hour hand — it needs a longer reach to read against the 24-hour bezel/track and a specific tube to fit the GMT pinion. Order GMT-specific hand sets when using NH34.

Skeleton movement ↔ skeleton dial / open front

NH7x movements expose the wheel train and balance from the dial side. They are NOT designed to be hidden behind a solid dial. Using NH70 with a standard solid NH35-compatible dial will block the visual appeal of the movement and is rarely the right choice. NH7x is for builds where the front of the watch shows the movement.

Hand Type M vs Type L

NH3x movements come in two hand-mounting heights: Type M (standard) and Type L (high-hand version with a taller cannon pinion stack). The two are visually similar but the hands sit at different heights above the dial. This affects:

• Crystal clearance: with Type L hands sitting higher, you need more crystal clearance — the second hand can foul a low-domed crystal
• Hand-to-dial gap: Type L hands clear printed dial elements that might catch Type M hands

Modder cases usually specify which Type they're built for. Lucius Atelier and most aftermarket cases use Type M. Confirm before ordering hands.

Stem length and crown type

Stem part 351-200 (tap 10) is the stock NH3x stem. Different case designs need the stem cut to length at assembly. Crowns come in screw-down (SKX-style) and push-in variants; mismatching crown type and case-tube tap is a real and common error. Always confirm the case's crown-tube tap before ordering a crown.

What to order this movement family for

• NH35A for a 3-hander with date — the broadest case/dial/hands ecosystem
• NH36A for day-date displays — used heavily for Submariner-style mods that show day+date
• NH38A for clean 3-hander, no date display under a solid dial; also for builds where the open balance wheel at 9 should be visible through a sapphire caseback
• NH34A for GMT — second time zone or 24-hour bezel watches
• NH70/71/72A for skeleton open-front watches where the movement is the visual centerpiece

Where to buy

These are wholesale movements without a Seiko-branded retail channel. Common sources:

• Esslinger (US) — esslinger.com — carries Hattori NH3x movements, US-domestic shipping, typically $80–$110 USD per movement. Apply Esslinger's "Select watch movements up to 20% off" coupon code if visible at checkout.
• Cousins UK — cousinsuk.com — carries the full NH3x and NH7x range with detailed product pages. Cross-border to the US; account-gated pricing on some movements.
• AliExpress modder sellers — many sellers carry NH3x at $25–$45 USD with mixed authenticity. Verify Japan or Malaysia rotor stamp; China-stamped rotors are not TMI-direct. Counterfeit NH35-style movements exist; price-anomaly check (a "NH35" under $20 is suspect).
• Crystaltimes (US) — usa.crystaltimes.net — carries NH3x at slightly above Esslinger pricing with better web UX.

Authoritative source documents (download direct from TMI)

• TMI NH35 spec sheet (official PDF)
• TMI NH36 spec sheet (official PDF)
• TMI NH36 operation manual (official PDF)
• TMI NH72 technical guide (official PDF)
• TMI 2026 catalogue (official PDF)
• TMI mechanical movement product page
• TMI skeleton mechanical product page

Community references (transcribed and discussed)

• Caliber Corner — full caliber index — most reliable secondary source for movement specs; transcribes TMI sheets with photos and discussion
• DIY Watch Club blog — NH34A specs
• DIY Watch Club blog — NH34A vs NH35A compatibility
• WR Accessories NH3x movement parts database — useful for cross-referencing which sub-parts (cannon pinions, winding wheels, stems) are shared across variants

Page maintained by Rob's timepieces project. Verified 2026-05-11 against the sources cited inline. If you spot drift between this page and the primary TMI source documents, the primary TMI source wins — file a correction in the repo at reference/movements/nh3x.md.