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When it comes to Seiko modding, one name continues to define reliability, accuracy, and pure mechanical joy — the Seiko NH movement. Whether you’re building your first custom mod or perfecting your tenth, chances are the beating heart inside your case proudly carries the “NH” signature.
My upgraded Seikonaut 38mm Titanium Ultra Thin Edition — the evolution of my daily Seikonaut 36mm Turquoise Mod.
The story of Seiko’s NH movement series begins with the company’s long pursuit of dependable, everyday mechanical timekeeping.
In the late 2000s, Seiko Instruments Inc. (SII) — the branch of Seiko responsible for movement production — recognized a growing demand beyond its own brand. Independent watchmakers, microbrands, and the emerging modding community needed a movement that was robust, affordable, and easy to integrate into custom designs. Seiko already had such a foundation in its in-house 4R series, a line of automatic movements celebrated for their reliability and straightforward construction.
By 2011, Seiko began offering a parallel lineup — the NH series — designed for external use. Mechanically, these calibres mirrored their 4R counterparts: for example, the NH35 shares the same base architecture as the 4R35, the NH36 with the 4R36, and so on. But instead of being reserved for Seiko-branded watches, the NH line was supplied to third-party manufacturers worldwide.
This subtle move changed the landscape of affordable mechanical watchmaking. Suddenly, modders and small brands had access to a Japanese-engineered, automatic movement with hacking and hand-winding — features once limited to higher-end pieces. The NH series delivered industrial reliability without the prestige markup of Swiss calibres like the ETA 2824 or Sellita SW200.
Over the years, Seiko’s NH movements became the heartbeat of countless microbrands and custom builds, earning a reputation for their durability and flexibility. The simplicity of their design meant parts were easy to source, assembly was forgiving, and accuracy could be fine-tuned with basic tools — a dream combination for watch modders.
Even today, more than a decade after its introduction, the NH family continues to define the modding world. Whether it’s a no-date field watch, a day-date diver, or a skeletonized showcase, the NH movement remains the reliable workhorse that powers creativity. It represents not just a chapter in Seiko’s history — but the foundation of a global community that builds, experiments, and celebrates the art of mechanical watches.
Originally developed by Seiko Instruments Inc. (SII), the NH movement family — such as the NH34, NH35, NH36, NH38, NH70, NH71, and NH72 — has become the industry standard for modders worldwide. Built with the same DNA as Seiko’s 4R series, these automatic calibres combine bulletproof durability, excellent timekeeping, and ease of servicing — a trio of qualities that have made them legendary.
While many microbrands have adopted Swiss or Chinese movements, Seiko’s NH calibres remain the gold standard for those who value true Japanese reliability.
My Seikonaut 36mm Turquoise Mod has been my daily companion since 2022 — my go-to watch for almost three straight years. It has travelled with me, endured humid days, accidental knocks, and countless wrist shots. Recently, I decided it deserved an upgrade — I rebuilt it into the Seikonaut 38mm Titanium Ultra Thin Edition, a lighter and more refined case and bracelet combo, all while retaining the same beloved turquoise dial, handset, and the ever-faithful NH38 movement inside.
Over the years, this timepiece has seen its fair share of adventures — and one rather unconventional cleaning experiment. Out of sheer curiosity (and perhaps a little laziness), I once put my Seikonaut into the dishwasher — yes, a full intensive wash cycle at 70°C, complete with a Finish tablet. The wash was powerful, the heat was intense… yet to my surprise, the entire watch came out perfectly fine — sparkling, squeaky clean, and running as if nothing had happened.
⚠️ Disclaimer: I did this purely for fun and was fully prepared to risk my timepiece. Please do not put your watch in a dishwasher. You could easily damage or destroy it. If you try this, you do so entirely at your own risk.
What continues to amaze me, however, is the resilience of both the design and the movement. After over three years of continuous wear — and even a 70°C dishwasher cycle — the watch still performs flawlessly. When I placed it on the timegrapher, the result was ±0 seconds per day. That’s Seiko engineering at its finest.
Timegrapher reading of ±0 seconds/day — proof of NH35’s precision even after years of wear.
| Movement | Functions | Finish | Notes |
|---|---|---|---|
| NH34 | GMT + Date | N.A. | Perfect for dual-time builds |
| NH35 | Date | N.A. | Most common and reliable all-rounder |
| NH36 | Day-Date | N.A. | Classic choice for SKX mods |
| NH38 | Open Heart / No Date | Polished Silver | Best for open-heart or clean no-date dials |
| NH70 | Skeleton | Silver | Full-view mechanical design |
| NH71 | Skeleton | Gilt / Yellow Gold | Vintage-inspired warm tone |
| NH72 | Skeleton | Ruthenium Grey / Gunmetal | Modern dark finish with depth |
While Seiko’s NH series reigns supreme in the modding world, it often gets compared to other well-known automatic calibres such as the ETA 2824-2 and Sellita SW200. These Swiss movements are celebrated for their precision and heritage — but they come at a much higher price point, often three to five times more expensive than a Seiko NH calibre.
Despite that price gap, the real-world performance difference is surprisingly small. In fact, many modders and microbrand builders choose the NH series precisely because it delivers 80–90% of the performance at a fraction of the cost.
The NH movements are engineered for endurance. Their robust gear train, metal construction, and simple architecture make them exceptionally resistant to shocks and easy to service — a major advantage for everyday watches and tool-style builds.
Swiss calibres like ETA or Sellita, while beautifully made, are also more delicate. They require tighter manufacturing tolerances and more frequent servicing, which increases long-term ownership cost. The NH series, on the other hand, is known to run reliably for years with little maintenance — a quality that’s hard to beat.
Out of the box, the NH35 or NH38 typically runs within –20 to +40 seconds per day, but many can easily be regulated to within ±5 seconds per day. In everyday use, this difference becomes negligible compared to a standard-grade ETA 2824-2 or SW200, both rated at around ±12 seconds per day.
What’s even more impressive — my own NH38-powered Seikonaut 38mm Titanium Ultra Thin Edition still runs at ±0 seconds per day, after over three years of continuous wear. For a movement that costs about USD 60–70, that level of consistency is astonishing.
Another major advantage of the NH family is its accessibility. Replacement parts, spare movements, and technical diagrams are widely available and affordable. Most independent watchmakers are familiar with the Seiko platform, and even hobbyists can learn to regulate or swap movements without needing expensive equipment.
Because of the low cost, if an NH movement ever becomes damaged — for example from water intrusion or a hard drop — it’s usually cheaper to replace the entire movement than to send it for an overhaul service. This practicality is one of the key reasons microbrands and modders gravitate toward Seiko’s NH series. It’s simple, dependable, and economically sensible.
The NH line isn’t just functional — it’s also visually flexible. Modders can choose between different functions and finishes, all sharing the same base design:
For independent modders and small-batch watchmakers, cost efficiency matters. An NH35 typically retails for USD 40–70, while a Sellita SW200 or ETA 2824-2 can cost USD 200–400 depending on grade and supplier.
That price difference allows creators to invest more into cases, dials, crystals, and finishing — the visible parts that make a watch special — without compromising on reliability. It’s the reason so many microbrands build their entire lineup around Seiko NH movements.
| Movement | Origin | Accuracy (factory) | Power Reserve | Average Price (USD) | Best For |
|---|---|---|---|---|---|
| Seiko NH3x / NH7x | Japan | –20 ~ +40 s/day | 41 hours | 40–70 | Modding, microbrands, daily wear |
| Sellita SW200-1 | Switzerland | ±12 s/day (standard) | 38 hours | 250–300 | Mid-tier Swiss watches |
| ETA 2824-2 | Switzerland | ±12 s/day (standard) | 38 hours | 300–400 | Luxury and heritage models |
Ultimately, Seiko’s NH series offers unmatched value for money. It delivers consistent accuracy, long-term dependability, and versatility — all at a fraction of the cost of its Swiss rivals.
For modders, that means more creativity and freedom.
For collectors, it means years of trouble-free mechanical satisfaction from a movement that truly punches above its price.
The NH movement represents more than just a mechanism; it’s the soul of Seiko modding. Reliable, precise, and endlessly customizable, it allows every builder to express creativity while trusting that the watch will run flawlessly for years to come.
So whether your next project is a diver, pilot, or field mod — choose a Seiko NH.
It’s not just a movement.
It’s a legacy of precision.
Tags: Seiko NH35, NH36, NH38, NH72, NH34 GMT, Seiko mod parts, Seiko modding, automatic movement, timegrapher, Lucius Atelier
