Two numbers define an enormous slice of the automatic watch market: NH35 and NH36. Manufactured by TMI — Seiko’s movement-supply subsidiary — they are the unbranded equivalents of Seiko’s own 4R35 and 4R36, sold to independent watchmakers around the world. Understanding what they are, where they come from, and how to look after them is the first step to buying any watch that runs on one.
Specifications sourced from TMI technical documentation via calibercorner.com (last modified 2026-10-14). Pricing from watchscanning.com (October 2026).
TL;DR
- NH35A: date only; 21,600 bph (3 Hz); 41 h power reserve; 24 jewels; hacks and hand-winds; 27.40 × 5.32 mm.
- NH36A: same base movement, adds day display at 3 o’clock.
- Both are made by TMI (Time Module Inc.), a Seiko subsidiary; sold to third-party watchmakers.
- Seiko’s own Seiko 5 Sports watches use the branded equivalents: 4R35 (date only) and 4R36 (day + date).
- Factory accuracy spec: −20 to +40 s/day; well-regulated examples commonly achieve −5 to +10 s/day.
- Service interval: approximately once every two to three years (Seiko recommendation).
In This Article
What Are the NH35 and NH36?
The NH35A and NH36A are automatic calibres manufactured by Time Module Inc., a wholly owned subsidiary of Seiko that exists specifically to supply movements to independent watchmakers. TMI sells to any qualified manufacturer willing to meet its minimum order volumes, which is how the same movement architecture powers everything from a $200 entry-level microbrand diver to limited-edition collaborations retailing above $500.
The two calibres share the same base plate and train. The NH35A features date-only display at 3 o’clock; the NH36A adds a day wheel alongside the date, displayed in a combined day-date window. Both movements hack — meaning the seconds hand stops when the crown is pulled to the time-setting position — and both can be hand-wound, a feature the earlier 7S26 (the ancestor of the NH35/NH36 architecture) notably lacked. Those two additions made the NH series considerably more user-friendly than what preceded them.
TMI is not a separate design house. The NH35A and NH36A are built to the same specifications as Seiko’s own 4R35 and 4R36 calibres that appear in the branded Seiko 5 Sports range. The practical difference between an NH36 and a 4R36 is that one leaves the factory with “NH36” engraved on the rotor and the other does not — the parts, the tolerances, and the manufacturing process are the same.
Specifications at a Glance
The table below summarises the core specifications for both calibres as documented by TMI.
| Specification | NH35A | NH36A |
|---|---|---|
| Complications | Date at 3 o’clock | Day + Date at 3 o’clock |
| Frequency | 21,600 bph (3 Hz) | 21,600 bph (3 Hz) |
| Power Reserve | 41 hours | 41 hours |
| Jewels | 24 | 24 |
| Accuracy (factory) | −20 to +40 s/day | −20 to +40 s/day |
| Hacking | Yes | Yes |
| Hand-winding | Yes | Yes |
| Diameter | 27.40 mm | 27.40 mm |
| Height | 5.32 mm | 5.32 mm |
The 4R35 and 4R36 Connection
When Seiko introduced its self-winding movement range for the refreshed Seiko 5 Sports in 2019, the new calibres carried the 4R designation: 4R35 for date-only models, 4R36 for day-date. At the same time, TMI continued offering the identical mechanisms to third-party brands under the NH35A and NH36A names. The relationship is straightforward: NH = 4R, unbranded.
This means a Seiko 5 Sports running the 4R36 and an independent microbrand diver powered by the NH36A are running essentially the same mechanism — from the same production line, to the same tolerances. The distinction matters for servicing (a Seiko-authorised centre will service the 4R but not necessarily an NH in a third-party case) and for resale positioning, but the mechanical experience is effectively identical.
It is worth noting that the NH35 and NH36 were preceded by the 7S26 and 7S36, which were also TMI-supplied movements but without hacking or hand-winding. Many vintage-style microbrands still reference the 7S-era architecture in their marketing; in practice, almost all current NH35/NH36 shipments are the NH35A and NH36A variants with those features added.
Accuracy in the Real World
The factory accuracy specification of −20 to +40 seconds per day is frequently misread as a description of typical performance. It is not. It is the tolerance band within which every unit that leaves the factory is guaranteed to operate — a legal specification designed to cover an entire production run of thousands of movements, not a prediction of what any individual watch will do on the wrist.
In practice, NH35- and NH36-powered watches in good condition, worn daily, typically settle between −5 and +10 seconds per day once the lubricants have distributed themselves over the first few weeks. Regulation is accessible to any watchmaker comfortable with the platform, and the architecture is well-understood given its widespread use. The movement is not a COSC-certified chronometer — that designation requires sustained performance within +6/−4 s/day — but it is not the wild deviation the spec sheet implies either.
If accuracy is a priority, Seiko’s higher-specification calibres offer a meaningfully different proposition. The 6R35 and 6R55 run at 23,600 bph with a factory spec of +10/−15 s/day and power reserves of 70 and 72 hours respectively. The upgrade in timekeeping performance is real, though it comes with a commensurate increase in the retail price of the watches that house them.
Which Watches Use Them?
Seiko’s own range. Every current Seiko 5 Sports uses the 4R36 (day + date) or 4R35 (date only). As of October 2026, US list prices for the range run from $315 for the SRPG35 and SRPJ85 Field Series at the entry point, to $450 for mid-tier references including the SSK023 and HDB003, up to $495 for the SSK001 and SSK003 GMT variants. The HDB006 and HDB007, the updated Field Series references launched in May 2026, retail at €390–€410 in Europe.
Microbrands and independent labels. TMI supplies the NH35A and NH36A to hundreds of independent watchmakers. Among the more visible names that have used them: Deep Blue’s Diver 1000 II uses the NH35A in a 44mm case; BOLDR’s Odyssey uses it in a tool-watch context. The NH38A — the same calibre without any date complication — is a frequent choice for brands favouring a cleaner dial. The movement’s footprint (27.40 mm diameter) fits comfortably in cases from 38 to 45 mm.
Service and Maintenance
Seiko recommends servicing the 4R-series calibres approximately once every two to three years. A full service covers cleaning the movement in an ultrasonic bath, replacing lubricants throughout the gear train and escapement, renewing the crown and case gaskets, and timing regulation on a timing machine. The movement’s parts are widely stocked by TMI distributors, which makes independent servicing straightforward for watchmakers familiar with Japanese calibres.
Official Seiko USA pricing for 4R-calibre service was listed at $154 as of April 2020; current rates should be confirmed directly with an authorised Seiko service centre, as labour costs have risen since that figure was published. For NH35- and NH36-powered microbrand watches, any qualified watchmaker experienced with Japanese movements can carry out a service, often at independent workshop rates below the authorised network.
Between services, the main practical steps are keeping the crown pushed in when not setting the time (to protect the crown tube), avoiding magnetic fields above the movement’s tolerance, and not pushing the hand-winding to resistance — the NH35/NH36 does not require manual winding in normal daily wear, and the clutch is not designed for sustained hand-winding sessions.
NH35/NH36 vs the Competition
The NH35 and NH36 compete directly with a handful of other movements that populate the same price bracket.
Miyota 8215/8217 (Citizen): Also at 21,600 bph, the 8215 lacks a hacking function and cannot be hand-wound — a notable limitation in everyday use. The 8217 adds a day display. Widely used at similar price points. Build quality and accuracy spec are roughly comparable to the NH35/NH36.
ETA 2824-2 and Sellita SW200: Both Swiss-made movements running at 28,800 bph, with a tighter factory accuracy specification (typically +/−12 s/day for standard grade), hacking, and hand-winding. Found predominantly in watches priced above $400. The higher frequency improves the smoothness of the seconds hand sweep and aids accuracy, but the watches housing these movements carry a correspondingly higher price premium.
Seiko NH38A: The no-date variant of the NH35A. Dimensionally identical, same specs — simply without the date wheel mechanism. Popular with brands that prioritise dial symmetry and a cleaner look below 6 o’clock.
At the NH35/NH36 price tier, the choice between Japanese and Swiss movements often comes down to what the watchmaker has built around them. A well-constructed case with good finishing on an NH36 beats a poorly finished case on an ETA 2824 at twice the price. The movement is one element; total value proposition matters more.
Where to Buy
For Seiko 5 Sports watches with the in-house 4R36, authorised Seiko retailers and department stores carry the full range, with pricing guaranteed to match the official list. Online, the Seiko brand is sold through major authorised marketplaces — search for current Seiko 5 Sports watches on Amazon for authorised listings. For pre-owned examples, our pre-purchase toolkit outlines what to check before buying any automatic watch on the secondary market.
For microbrand watches powered by the NH35A or NH36A, buying direct from the brand’s official site is the safest route. Grey-market NH-movement watches are common on auction platforms; condition varies considerably, and service histories are rarely available.
The NH35A is date-only: a single window at 3 o'clock showing the date. The NH36A adds a day wheel to that window, displaying both day and date side by side. Both movements share the same base plate, frequency (21,600 bph), power reserve (41 hours), and dimensions (27.40 × 5.32 mm). The only mechanical difference is the additional day disc and jumper mechanism in the NH36A.
The NH35A is manufactured by Time Module Inc. (TMI), which is a wholly owned subsidiary of Seiko. The movement is mechanically identical to Seiko's own 4R35 calibre used in branded Seiko 5 Sports watches — same parts, same tolerances, same factory. The NH designation appears on movements sold to third-party watchmakers; the 4R designation appears on movements Seiko retains for its own branded watches.
The factory specification is −20 to +40 seconds per day, which is a production guarantee covering the full range of units, not a prediction of typical performance. In practice, a healthy NH35 or NH36 worn daily typically runs between −5 and +10 seconds per day once broken in. If your watch is running significantly outside that range, it may need regulation or service. For comparison, Seiko's higher-spec 6R55 is factory-rated to +10/−15 s/day.
Seiko recommends servicing the 4R-series calibres (the branded equivalent) approximately once every two to three years. A full service covers cleaning, oiling, gasket replacement, and timing regulation. Official Seiko USA pricing for 4R service was $154 as of April 2020; confirm current rates with an authorised service centre. For NH-branded movements in third-party watches, any watchmaker experienced with Japanese calibres can perform the service.
In principle, yes — a watchmaker can swap the movement if a compatible replacement fits the case dimensions. The NH35A's 27.40 mm diameter and 5.32 mm height are shared by several other calibres. In practice, movement swaps are rarely cost-effective unless the case is high quality and the upgrade movement (such as a 6R35 or Miyota 9015) is priced reasonably. For most NH-based microbrand watches, buying a better watch outright makes more economic sense than a movement upgrade.
Final Verdict
The NH35 and NH36 are not the most accurate movements available at any price. What they offer is reliability, parts availability, a well-understood service path, and the credibility of originating in a Seiko-affiliated factory. For anyone entering the automatic watch market through a microbrand, they represent a reasonable mechanical foundation — better than much of what was available at equivalent prices a decade ago.
If you want Seiko’s own quality controls on the same mechanism, the Seiko 5 Sports with the 4R36 is the direct route. At $315–$495 US list, it remains one of the most competitive automatic watch propositions in that bracket. For the full picture on how Seiko watches hold their value over time, or the history of the movement’s lineage through the Seiko Prospex range, follow the links below.
Sources: calibercorner.com (last modified 2026-10-14, 2026-03-21); watchesbysjx.com (May 2026); watchscanning.com (October 2026); notebookcheck.net (August 2026); Seiko official product pages via seikowatches.com/nz-en/ and seikowatches.com/in-en/ (November 2026).
