The Complete Seiko NH34 GMT Movement Guide
What “GMT” really means – and why the NH34 owns the modding world.
GMT stands for Greenwich Mean Time, now technically UTC, but the watch world refuses to let the old name die. In modern horology, a “GMT watch” means a timepiece that shows two time zones at once – local time on the main hands plus a second “reference” zone (home, office, UTC, family, etc.) on a dedicated 24-hour GMT hand. Ever since its launch in mid-2022, the Seiko NH34 has become the undisputed king of this complication for modders: it delivers genuine caller GMT functionality in the same drop-in footprint as the NH35/NH36, yet costs only $20–$30 more. For the price of a decent lunch, you now get an independently adjustable 24-hour hand that used to be the preserve of $500+ Swiss movements – and that perfect blend of compatibility, reliability, and Seiko quality is exactly why the NH34 powers the vast majority of aftermarket GMT builds you see today.
When Was the NH34 Released?
The Seiko NH34A, also known simply as the NH34, debuted in the aftermarket world in mid-2022, just a few months after Seiko unveiled its branded counterpart, the 4R34, powering the entry-level Seiko 5 Sports GMT collection (like the SSK001, SSK003, and SSK005 models) back in June 2022. Announced on June 8, 2022, with global availability starting in July, those affordable factory GMTs (around $400–$450 retail) were a quiet revolution for everyday travellers and watch enthusiasts. But for us modders, the real fireworks happened shortly after when Seiko released the NH34 to third-party suppliers, and shelves emptied in days as everyone scrambled to snag one for under $80. Imagine finally having a drop-in GMT upgrade for your SKX or SRPD build without shelling out for pricier alternatives. Suddenly, that Explorer II homage or Black Bay tribute went from "nice idea" to "build it this weekend" reality.
NH34 vs 4R34
As for the subtle difference between the NH34 and the 4R34: They're mechanically identical in every way (same 27.4mm diameter, 24 jewels, 21,600 bph beat rate, and that 54° lift angle), but the 4R34 is Seiko's in-house version, always stamped "Japan" on the rotor for factory watches, while the NH34 is the unbranded export variant sold to mod shops and microbrands, sometimes produced in Malaysia or other facilities for broader supply. Modders often swear by the NH34 for its availability and slight edge in out-of-the-box accuracy. However, both are workhorses that hold up to daily abuse. By early 2023, it had become the go-to heart for affordable GMT mods, and even in 2025, it's still the most-stocked calibre at places like ours, proving Seiko nailed the timing for when modders were hungry for an accessible GMT movement.
The Main Feature – GMT
The standout feature of the NH34 is its caller (or office) GMT complication, which adds a dedicated 24-hour hand that can be set independently from the main timekeeping hands. Here's a straightforward breakdown of how it operates, especially useful if you're in the middle of a mod build and need to know exactly what you're working with.
When the crown is pulled to the first position, you can rotate it one way to quick-set the date and the other way to adjust the GMT hand in one-hour increments. This lets the GMT hand track a second time zone (like your home office or UTC) while the main hour and minute hands keep displaying your local time without interruption. The seconds hand continues ticking, so there's no loss of accuracy during setup. In the second crown position, you set the main time by adjusting the hour and minute hands together, just like on a standard NH35 or NH36.
For modders, this setup is a game-changer because it's dead simple and reliable—no fancy gears or extra complications that drive up the price or failure rate. Say you're assembling an SSK003 homage or a custom dual-time diver: you set the main hands to your current location, then dial in the GMT hand to monitor another zone, like calling back to the office without recalculating the math. It's not designed for constant time-zone hopping (you'd reset the main time to local when travelling long-term, then readjust the GMT hand to home), but for everyday use in a modded SKX or 5KX, it's spot-on—affordable, hackable, and tough enough for daily wear. That's why it's exploded in popularity since 2022; you get dual-time tracking without the premium cost of alternative calibres, making high-end GMT homages accessible for under $80 in movement costs alone.
Full Technical Specifications
| Specification | NH34A (4R34) |
|---|---|
| Diameter | 27.4mm |
| Height | 5.32mm |
| Jewels | 24 |
| Frequency | 21,600 bph (6 beats/sec) |
| Power reserve | ~41 hours |
| Lift angle | 54° (critical for timegrapher) |
| Hour hand diameter | 1.5mm |
| Minute hand | 0.9mm |
| GMT hand | 2.2mm |
| Seconds hand | 0.21mm |
| Hacking seconds | Yes |
| Manual winding | Yes |
| Date wheel overlay | Same as NH35/NH36 |
| Shock protection | Diashock |
| Typical accuracy (stock) | –15 / +25 seconds per day |
Compatibility – Cases, Dials & Hands
Because the NH34 shares the exact dimensions and mounting points with the NH35/NH36 family, it is a 100% drop-in replacement for any case on the market that accepts those movements. We test them daily in our SKX conversion case series. Any dial designed for an NH35 will fit perfectly. The date window sits in the identical 3 o’clock position. For the GMT hand, virtually every aftermarket option fits without modification.
Most Common Questions Answered
What is the lift angle of the Seiko NH34 or 4R34?
The lift angle is 54°. Always set your timegrapher to 54° before diagnosing your movement.
Will an NH34 fit in an SKX007 / SRPD / 5KX case?
Yes, 100 %. The NH34 has identical outer dimensions and mounting points to the NH35 and NH36, so it is a direct drop-in replacement.
Do I need a special date wheel or overlay for the NH34?
No. It uses the same date wheel overlay as the NH35 and NH36.
Is the NH34 the same as the Seiko 4R34?
Yes, they are identical movements. “NH34A” is the aftermarket designation; “4R34” is the internal Seiko factory designation.
What are the correct hand sizes for the NH34?
Seconds: 0.21 mm
Minute: 0.9 mm
Hour: 1.5 mm
GMT: 2.2mm
Can I use regular NH35 dials with the NH34?
Yes, but if you are using a standard NH35 dial, widen the centre hole to ~2.4–2.9mm to clear the taller GMT pinion stack (easy with a needle file). Aftermarket dials are pre-sized and will fit. The date window position and dial feet are identical. NH36 are not compatible due to the day function.
Is the NH34 a “caller” GMT or “traveller” GMT?
It is a clock with GMT – you jump the GMT hand independently while the hour hand stays on your local time.
Where to Buy Genuine NH34 Movements in 2025
We keep factory-fresh, genuine Seiko SII/TMI NH34A movements in stock year-round with same-day shipping. Current price is $80.00 —Grab a genuine NH34.
Conclusion
Currently, the NH34 remains the undisputed king of affordable traveller GMT modding. Nothing else on the market gives you genuine caller-GMT dual-time functionality for under $80. Whether you are building a homage, a Black Bay GMT tribute, or a clean polar Explorer II, the NH34 is the heart of the watch.
Ready to start your build? Grab a genuine NH34 and drop your planned case/dial combo in the comments.