Building a custom watch starts with one choice that defines everything else: the movement. It decides your dial layout, your hand fitment, your case thickness, and even how your watch feels when you wind it.
If you’ve ever swapped dials or modded a Seiko SKX case, you already know: picking the right automatic movement isn’t about price — it’s about purpose.
In 2025, five movements dominate the custom-watch scene: Seiko NH35/NH36, Miyota 9015, ETA 2824 / Sellita SW200, and Sea-Gull ST36. Each has its own character, its own rhythm, and its own loyal following among modders, microbrands, and enthusiasts.
This guide breaks them down from real-world experience — how they feel, how they perform, and which one fits your next build. New to modding? Check out Everything You Need to Start Watch Modding.
1. Seiko NH35 – The Modder’s Workhorse
If you ask ten modders what their first build used, nine will say “NH35.” It’s the backbone of the entire custom-watch world — reliable, affordable, and endlessly compatible.
Why it dominates
- Drop-in fit for countless Seiko-style cases (SKX, SRPD, Turtle).
- Smooth 21,600-bph sweep that balances accuracy and durability.
- Supports hand-winding and hacking seconds — ideal for beginners.
- Works perfectly with aftermarket dials, crowns, and hands available from Sugargoo’s Seiko NH Series Movements.
Experience
It winds with a firm, mechanical click, and feels solid even after years of use. It’s not the quietest rotor, but its consistency is legendary. Learn why in Why NH35 Is Perfect for First-Time Builders.
Best for
- Dive watch mods
- Everyday builds needing reliability
- Learning how to assemble or regulate your first automatic watch
SEO-targeted phrases: Seiko NH35 automatic movement review, NH35 custom watch build, NH35 mod parts Taobao agent, Seiko NH35 movement compatibility.
2. Seiko NH36 – For Builders Who Want More Functionality
Think of the NH36 as the NH35’s twin — same case fit, same height, same durability — but with an added day complication.
If your dial shows both day and date, NH36 is your pick. It’s also fully interchangeable with most NH35 cases, hands, and crowns.
Why modders love it
- Adds day/date without increasing thickness.
- Smooth sweep and robust clutch system.
- Excellent parts availability through Sugargoo Watch Movements Collection.
User insight
The NH36 bridges practicality and personalization — you can swap to Kanji day wheels or custom font disks to give your build a subtle flair. See Fixing Date Wheel Misalignment in NH35 Watches for tips.
Best for
- Custom field watches
- Vintage-inspired daily wear
- Modders who like multi-language day wheels
SEO-targeted phrases: NH36 automatic movement comparison, Seiko NH36 modding guide, NH36 day-date replacement, NH35 vs NH36 explained.
3. Miyota 9015 – The Thin and Modern Choice
For modders who prefer slim, minimalist cases, Miyota 9015 is the go-to. It’s thinner than the NH35 by nearly a millimeter, which makes a big difference when designing custom cases.
Why it stands out
- High beat rate of 28,800 bph gives a smooth, luxury-grade sweep.
- Reliable unidirectional rotor (though you’ll hear it spin).
- Excellent accuracy out of the box — often +10 s/day.
- Common in microbrand watches for its slim profile.
How it feels
Wind it, and you’ll notice less resistance than the NH35. The seconds hand glides almost like a Swiss piece. Compare it in Miyota 8215 vs 9015.
Compatibility notes
It’s not drop-in compatible with Seiko NH-based cases — the stem height and dial feet differ. But many custom cases sold on Sugargoo Watch Cases list 9015 compatibility.
Best for
- Sleek custom dress watches
- Thin case builds with sapphire backs
- Builders upgrading from Seiko platforms
SEO long tails: Miyota 9015 mod build, 9015 vs NH35 thickness, best movement for microbrand custom watches, Miyota 9039 no-date version guide.
4. ETA 2824 / Sellita SW200 – The Swiss Standard
You can’t talk about watch movements without mentioning the ETA 2824. It’s the foundation for countless Swiss automatics — Tissot, Hamilton, and more.
But since ETA limited supply, Sellita stepped up with the SW200, an almost identical twin with one extra jewel and easier global access.
Why it’s respected
- High accuracy and stable amplitude.
- Smooth, silent rotor motion.
- Strong spare-parts ecosystem for repairs.
- 28,800 bph sweep — crisp and precise.
Modding perspective
It’s the choice when you want to build something that feels Swiss. It pairs beautifully with sapphire crystals, tight-tolerance crowns, and higher-end cases.
Buyers can find compatible options via: ETA Series Watch Movements and Sugargoo Watch Movement Parts.
Best for
- Premium builds and homage projects
- Users chasing Swiss accuracy in custom cases
- Professional microbrands needing consistent supply
Natural SEO embedding: ETA 2824 mod guide, Sellita SW200 vs ETA comparison, Swiss automatic movement for custom watch, ETA replacement options 2025.
5. Sea-Gull ST36 – The Mechanical Artist’s Choice
Not everyone wants an automatic rotor hiding their movement. The ST36, Sea-Gull’s manual-wind Unitas clone, turns winding into ritual.
You feel every click, every bit of torque entering the spring — it’s analog pleasure.
Why modders choose it
- Simple, open architecture perfect for skeleton or exhibition-back watches.
- 45-hour reserve with large balance wheel and low 18,000 bph beat.
- Affordable entry to visible horology.
It’s also a favorite for hand-wind training builds, where you learn torque control and escapement balance firsthand. Available through Chinese ST-Series Movements on Sugargoo — including bridge-decorated and gilt variants.
Best for
- Vintage or steampunk-style builds
- Skeleton-dial custom projects
- Manual-wind collectors who enjoy tactile feel
Long-tail coverage: ST36 manual movement modding, Sea-Gull ST36 replacement, hand-wind watch build guide, Chinese ST movement customization.
6. Choosing the Right Movement for Your Build
There’s no single “best” automatic movement — only the one that matches your vision. Here’s how to think about it:
- Building a diver or daily beater? Choose NH35 or NH36.
- Creating a thin, modern design? Go with Miyota 9015 or 9039.
- Chasing Swiss precision? ETA 2824 / Sellita SW200 delivers.
- Exploring traditional hand-wind craft? Pick the ST36.
Each movement defines your case dimensions, hand fitment, and even the modder community you’ll be part of. Join discussions at Watch Modding Communities.
Before ordering, check dial feet alignment and stem height on the Watch Movements Guide and cross-verify with your case listing on Watch Cases Replacement.
7. Modding Tips for Power, Accuracy, and Feel
- Regulate before assembly — use a timegrapher to fine-tune accuracy.
- Lubricate mainspring and rotor bearings — improves power reserve by up to 10%. See Watch Oils and Lubricants Explained.
- Replace gaskets when resealing — see Watch Case Gaskets for full kits.
- Use matching crown stems — incorrect length causes wobble or date-change issues. Check How to Replace a Watch Crown and Stem.
- Keep spare hands sets — not all manufacturers follow identical tolerances. Browse Watch Hands Replacement.
8. The 2025 Trend: Accessible Precision
The global supply of NH and Miyota movements keeps custom watch culture thriving. Meanwhile, more modders are experimenting with hybrid builds — mixing Seiko movements in bespoke Swiss-style cases, or swapping NH38 no-date variants into diver builds for a cleaner dial.
This blend of creativity and precision is what 2025 is all about: custom expression powered by proven engineering.
Sugargoo continues to make this easier by offering direct sourcing from Taobao and 1688, quality-check photos, and combined international shipping — making global modding accessible. Learn how in What Is a Taobao Agent? or explore How to Combine Multiple Orders on Sugargoo.
You can browse:
Each page interlinks so you can plan your full build — from rotor to bracelet — without leaving the ecosystem. For quality assurance, see Sugargoo’s QC Service Guide.
9. Final Thoughts
Choosing a movement is like choosing a language — it defines how your watch speaks. The NH35 tells a story of reliability, the Miyota 9015 whispers refinement, and the ETA 2824 speaks fluent precision. Whichever one you choose, understand its rhythm, respect its design, and build something that feels alive on your wrist.
Because behind every custom watch isn’t just a movement — it’s a maker learning to master time itself. Ready to start? Explore DIY Watch Assembly for Beginners or join the community at Sugargoo’s Watch Parts Collection.
