Seiko Automatic Movements for Mod Builds

Seiko TMI Automatic Movements — NH34 GMT, NH35, NH36, NH38 & NH71

Find genuine Seiko automatic movements for your Seiko mod build from 9 options at Watch&Style. Every movement in this collection is labeled "Seiko (TMI)" — manufactured by Seiko Time Module Inc., Seiko's official movement subsidiary (also known as Seiko Instruments Inc. / SII) that produces the NH-series "Basic Mechanical Series" calibers used across the modding industry. Whether you're sourcing a workhorse NH35 for a daily-wear build, a day-date NH36 for a vintage SKX-style project, an NH34 GMT for a travel watch, an NH38 for a clean no-date dial, or an NH71 skeleton for an open-display build, this is where you find the heart of your Seiko mod.

Movement Calibers Explained

The collection covers five distinct NH calibers, each optimized for a different build aesthetic. The NH35 is the workhorse of the lineup — three hands plus date, 24 jewels, 21,600 bph, 41-hour power reserve, with hacking seconds and hand-winding. The NH36 adds a day-date complication to the NH35 architecture and is offered in both 3 o'clock and 3.8 o'clock crown variants to match your case's crown position (the day wheel orientation differs between the two). The NH34 is the GMT variant — a "caller GMT" with an independently adjustable 24-hour hand, designed for SSK Seiko 5 GMT builds and SKX/SRPD GMT mods, with the same 41-hour power reserve and proven NH reliability. The NH38 removes the date complication entirely for clean, symmetrical no-date dials — popular for minimalist and open-heart builds with no ghost crown position. The NH71 is the gold-plated skeletonized variant of the NH35 — 24 jewels, fully exposed mainplate, bridges, and balance wheel, with Côtes de Genève finishing on the rotor for premium open-display builds with exhibition casebacks.

Crown Position & Movement Selection

For NH36 movements specifically, the crown position of your case determines which day wheel orientation you need. A case with a 3 o'clock crown requires the NH36A (3 o'clock crown case) variant — the day wheel is oriented to align correctly when the crown sits at 3 o'clock. A case with a 3.8 o'clock crown (or "4 o'clock" crown in casual reference, as used on stock SKX007 builds) requires the NH36A (3.8 o'clock crown case) variant. Installing the wrong crown-position variant will cause the day to display off-center in the dial's day window. Match your movement to your case before ordering.

Movement Specifications & Build Compatibility

All NH-series movements in this collection share core specifications: 24 jewels, 21,600 beats per hour, 41-hour power reserve, bidirectional automatic winding via Magic Lever, hacking seconds, and hand-winding capability. Diameter is 27.4mm (29.36mm with spacer) and thickness is 5.32mm across the NH35/NH36/NH38/NH71 family; the NH34 GMT shares the same dimensions but has a 0.4mm taller hand stack on the dial side that affects crystal and dial fitment. Pair your movement with matching cases, dials, hands, chapter rings, crystals, crowns, and other mod parts from adjacent collections to complete your Seiko mod build.

Frequently Asked Questions

What's the difference between NH35 and NH36?

The NH35 has a date complication only; the NH36 adds a day complication for the classic SKX007-style day-date layout. Both share the same dimensions, power reserve, frequency, jewel count, and reliability — the difference is purely the dial-side day wheel. If you're building a date-only dial, choose the NH35. If you're building a vintage SKX-style day-date dial, choose the NH36 in the crown position matching your case.

What's the difference between NH38 and NH35?

The NH38 is the NH35 architecture with the date complication removed entirely. This creates a cleaner movement with no "ghost" crown position when setting the time, and a more symmetric layout for skeleton dials and minimalist no-date builds. Approximately 90% of parts are shared between NH38 and NH35; the difference is only the calendar module.

Will an NH34 GMT movement drop into my SKX007 case?

The NH34 has the same outer dimensions as the NH35/NH36 (27.4mm × 5.32mm) and fits cases designed for that footprint. However, the NH34 has a 0.4mm taller hand stack and a wider dial center hole requirement (2.88mm vs. 2.05mm for standard NH35 dials). This means standard NH35 dials require modification to fit NH34, and flat crystals may interfere with the seconds hand — most NH34 builds use a double-dome crystal and a GMT-specific dial pre-sized for the NH34 pinion stack.

Browse the full Seiko TMI movement collection above to find the caliber that powers your next Seiko mod build.