What to Know Before Building Your 37mm Royal Oak Seiko Mod

Meta Description: Considering a 37mm Royal Oak Seiko Mod? Learn everything you need to know before buying—from essential tools and crystal coatings to bracelet care and sizing tips.

A New Standard in Seiko Modding

When Nomods launched in 2024, we had a clear mission: create premium watch cases in sizes that actually fit most wrists.

The watch world is shifting. Collectors are moving away from oversized designs and embracing more modest proportions. Yet the modding community has been stuck with cases that rarely dip below 40mm.

We changed that.

Our 37mm Royal Oak case—affectionately known as the Seikoak—is the first high-quality sub-40mm Royal Oak-style case designed specifically for Seiko modding. It pairs the iconic octagonal silhouette with dimensions that wear comfortably on virtually any wrist.

Whether you're building your first mod or adding to a collection of custom pieces, this guide covers everything you need to know before starting your Seikoak project.

Essential Tools for Your Build

Assembling a Seikoak is straightforward—no more complex than any standard Seiko mod. But having the right tools makes the difference between a frustrating experience and a satisfying build.

What you'll need:

Caseback screwdriver — Our cases use screw-down casebacks for improved water resistance. A quality screwdriver with the correct blade width prevents slipping and scratching.
Precision screwdriver set — Required for removing bracelet links and adjusting fit. The integrated bracelet uses small screws that demand proper tools.
Soft work surface — A microfiber cloth or watch mat protects your case from scratches during assembly.
Movement holder (optional but recommended) — Keeps your NH35, NH36, or NH72 secure while installing the dial and hands.

Investing in proper tools isn't just about convenience—it's about protecting your build. Stripped screws and scratched cases are almost always the result of using the wrong equipment.

A Note on Plated Cases

Choosing a gold or rose gold PVD-plated Seikoak? You're getting more than just a striking finish—you're getting a case that's been through a multi-step electroplating process for lasting durability.

However, during plating, small amounts of residue can settle in the bracelet screw threads. Before sizing your bracelet, take a few minutes to clean it properly:

Rinse the bracelet in warm water with a drop of mild dish soap
Use a soft brush to gently clean around the screw heads
Dry completely with a lint-free cloth
Then proceed with link removal

This simple step ensures screws turn smoothly and preserves that flawless plated finish. Skip it, and you risk stuck screws or surface damage from forcing.

Blue AR vs. Clear AR: Choosing Your Crystal Coating

Every 37mm Seikoak comes with a sapphire crystal featuring anti-reflective coating. You'll choose between two options—and the right choice depends on your dial and aesthetic preferences.

Blue AR Coating

Blue AR produces a subtle blue shimmer under bright light—the same effect you'll find on high-end Swiss timepieces. It's understated in normal conditions but catches the eye when light hits at certain angles.

Best paired with:

Black, silver, or navy dials
Meteorite or textured grey finishes
Builds aiming for that luxury Swiss aesthetic

Clear AR Coating

Clear AR is virtually invisible. No tint, no shimmer—just pure optical clarity. The crystal disappears, letting the dial speak for itself.

Best paired with:

Skeleton NH72 movements where you want maximum visibility
Colourful dials in green, red, or champagne that might clash with blue tones
Minimalist builds where any colour distortion feels wrong

Neither option is objectively better. Blue AR adds character; Clear AR stays neutral. Choose based on what serves your build.

The Half-Link: A Small Part That Makes a Big Difference

Integrated bracelets look fantastic—but they present a sizing challenge. Unlike watches with removable end links and interchangeable straps, integrated designs require precise link adjustment for proper fit.

Standard full links sometimes remove too much length. Leave one in, and the bracelet feels loose. Take it out, and it's too tight.

That's why we developed the 37mm Royal Oak Half-Link—a custom 1.5x link that sits between full link increments. It provides the fine-tuning that integrated bracelets demand, especially for smaller wrists where every millimetre matters.

If you're between sizes with the standard bracelet, the half-link solves the problem. We recommend adding one to your order—it's a small investment that significantly improves wearability.

Movement Compatibility

The 37mm Seikoak case accepts all standard Seiko NH-series movements:

NH35 — Time-only with date at 3 o'clock
NH36 — Adds day-date complication
NH38 — Time-only without date window
NH72 — Skeleton movement for open-dial builds

All movements share the same dimensions, so you can choose based on your preferred complications and aesthetic. Skeleton builds with the NH72 have become particularly popular—the open caseback and dial-side visibility create a watch that's as interesting to look at as it is to wear.

Why 37mm?

We didn't choose 37mm arbitrarily.

First, it simply wears better. The Royal Oak's angular case and integrated bracelet create visual presence that doesn't require oversized dimensions. At 37mm, the Seikoak sits proportionally on wrists from 6 inches to 7.5 inches without looking undersized or overwhelming.

Second, it's practical. The case slips under shirt cuffs effortlessly—something that can't be said for 42mm+ alternatives.

Third, it aligns with industry direction. Luxury brands are reintroducing smaller references, and vintage-sized pieces are commanding premiums at auction. The 37mm Seikoak positions your build ahead of this curve.

Ready to Build?

The 37mm Royal Oak Seiko Mod case represents what we believe modding should be: accessible luxury in proportions that make sense.

Whether you're after a blacked-out stealth build, a gold skeleton showpiece, or a clean daily wearer in steel, the Seikoak platform delivers. Pair it with your choice of dial, hands, and movement to create something entirely your own.

Explore the 37mm Royal Oak Case →

Browse compatible dials, hands, and movements →

Questions before you buy? Our team is here to help with your next build.

Check out our Seiko mods.