The most common first question for new Seiko modders isn't about dials or cases: it's which movement to use. The NH35 and NH36 are nearly identical, but the difference matters once you're choosing a dial. Use the Assemble Watches Seiko mod builder to visualize either movement in your build before committing.
Quick Comparison
| Feature | NH35 | NH36 |
|---|---|---|
| Complication | Date only | Day + date |
| Movement height | 5.32 mm | 5.32 mm |
| Outside diameter | 27.40 mm | 27.40 mm |
| Casing diameter | 29.36 mm with dial spacer | 29.36 mm with dial spacer |
| Frequency | 21,600 vph | 21,600 vph |
| Power reserve | ~41 hours | ~41 hours |
| Hacking / hand-wind | Yes / Yes | Yes / Yes |
| Jewels | 24 | 24 |
| Dial feet | Standard Seiko | Standard Seiko |
| Typical price | £20–£35 / $20–$35 | £30–£45 / $30–$45 |
When to Choose the NH35
The NH35 is the right choice for most first builds. It uses the same published height and footprint as the NH36, so the decision usually comes down to the dial. The NH35's date-only display means a wider selection of compatible dials: most aftermarket dials are cut for the NH35, and date-only apertures tend to look cleaner because they are smaller and less visually dominant.
Cost is a minor but real advantage too. The NH35 typically runs £10–£15 less than the NH36, which adds up if you're planning multiple builds or experimenting with different parts combinations before committing.
In practical terms: if you don't have a strong preference for seeing the day of the week on your watch, or if your dial of choice is NH35-cut, the NH35 is the safer default.
When to Choose the NH36
The NH36 makes sense when the day display is something you'll actually use. It's a small thing, but if you wear a watch as your primary time-telling device and you find yourself glancing at the day window regularly, the NH36 earns its slight premium. It's also the more common choice for field-watch-style builds, where the fuller date and day complication fits the utilitarian aesthetic.
Case fit is usually the same for both movements because TMI lists the same outside diameter, casing diameter, and total height for the NH35A and NH36A. Where you still need to check carefully is the dial and date window: an NH36 needs a day-date aperture, while an NH35 only needs a date aperture.
One practical note: the NH36's day wheel often defaults to English, but the wheel itself is interchangeable. Alternative language day wheels are available separately if you want something different.
What About the NH70 and NH71?
The NH70 and NH71 are worth knowing about if you're planning a no-date build. Both share the same footprint as the NH35 and NH36, so they drop into the same cases and accept the same hands.
The NH70, NH71, and NH72 are skeleton movements based around the same NH family architecture. They have no date or day display, use three hands, run at 21,600 bph, and include stop seconds. The practical difference is mostly finish: NH70 is the silver option, NH71 is gilt, and NH72 is a darker gray finish. They are useful when the movement is meant to be seen through the dial, not hidden behind it.
| Spec | NH35 | NH71 |
|---|---|---|
| Date complication | Yes | No |
| Day complication | No | No |
| Skeleton / open-heart dial | No | Yes |
| Movement diameter | 27.40 mm | 27.40 mm |
| Movement height | 5.32 mm | 5.32 mm |
| Dial required | Date-cut dial | No-date or exhibition dial |
Both share the same case footprint and hand tube sizes, so the choice comes down to whether you want a date window (NH35) or a clean, no-date skeleton dial (NH71). See the NH71 compatible dials reference for confirmed and probable dial matches.
Movement Variants: NH71 and NH36A
Planning an NH71 build? The NH71 drops into the same cases as the NH35 and NH36, so an NH71 build follows the same compatibility rules — just paired with a no-date dial. Try the NH71 in the builder.
What is the difference between the NH35 and NH71?
The NH71 is Seiko's non-date movement — it uses the same NH-series footprint as the NH35 but removes the date complication entirely. This makes it compatible with no-date dials and cleaner dial designs that don't need a date aperture. If you want a no-date build with an NH-series movement, the NH71 is the standard choice. Everything else — hacking, hand-winding, power reserve, case compatibility — is the same as the NH35.
What is the difference between the NH36 and NH36A?
NH36 is the movement family name and NH36A is the common variant sold for Seiko mod builds. For practical modding purposes, treat NH36 and NH36A as the same: both are day-date automatic movements in the NH-series footprint, run at 21,600 bph, use the same hand sizes, and fit the same cases. The important check is the dial: it needs a day-date aperture, not an NH35 date-only aperture.
Should I use the NH71 or NH35 for my Seiko mod?
Choose the NH71 if you want a no-date dial or a cleaner dial design without a date aperture. Choose the NH35 if you want a date function — it has the widest selection of compatible aftermarket dials. Both share the same case footprint and part compatibility. The NH71 build is popular for field watch and tool watch aesthetics where a date complication is unwanted.
Can I use an NH71 movement in a Seiko mod?
Yes. The NH71 is a skeleton automatic movement from TMI (the same manufacturer as the NH35 and NH36) with an identical 27.40mm diameter and 5.32mm height. It fits any case that accepts the NH35 or NH36. The main considerations: the NH71 has no date complication, so you need a no-date or exhibition dial, and the exposed rotor adds to the visual character of the build.
What cases are compatible with the NH71 movement?
The NH71 uses the same case footprint as the NH35 and NH36 — 27.40mm movement diameter, standard Seiko NH casing dimensions. This means it fits SKX007-spec aftermarket cases, SRPD-style cases, and any case listed as NH35-compatible. Check that the caseback allows exhibition viewing if that's the goal; many SKX-style cases have solid casebacks.
Which Movement Does Assemble Watches Support?
The Assemble Watches builder supports both the NH35 and NH36. Select your movement at the start of the build flow and the builder will filter compatible dials, cases, and hands automatically, including flagging dial aperture mismatches between NH35-cut and NH36-cut dials.
Frequently Asked Questions
Is the NH35 or NH36 more reliable?
Both are equally reliable. They share the same movement architecture, frequency, power reserve, and jewel count. Reliability differences between individual units are normal manufacturing variance, not a fundamental difference between the two calibres.
Can I use an NH36 in a case designed for an NH35?
Usually yes. TMI lists the NH35A and NH36A with the same outside diameter, casing diameter, and 5.32mm total height. The part you need to check is normally the dial: an NH36 needs a day-date aperture, while an NH35 only needs a date aperture.
Where can I see which movements are compatible with my chosen case?
Use the Assemble Watches builder. Select the case you're interested in and the builder will show which movements fit it, along with compatible dials and hands.
What's the price difference between NH35 and NH36?
The NH36 typically costs £10–£15 more than the NH35 from the same vendor. On current pricing this means roughly £30–£35 for the NH35 versus £40–£45 for the NH36. Prices vary by vendor and region.