NH35 Mod Kit: How to Build Your First Dive Mod

An NH35 mod kit, often called a Seiko mod kit, is a set of aftermarket parts built around a Seiko NH-family automatic movement, so you can assemble a watch that looks the way you want instead of buying one off the shelf. Here is what a dive mod kit includes, which parts fit together and the steps for your first build.

If you want everything in one box, our Prodi Dive Kit is a 40mm dive-style build with the movement, tools and a second dial included.

What is an NH35 mod kit?

It is a collection of case, dial, hands, bezel and crystal parts made to fit Seiko NH35-family movements. "Seiko mod" describes the style of build, not a watch made or sold by Seiko.

The hobby grew because the NH35 is reliable, affordable and well documented, and because so many parts makers design to its dimensions. A dive mod, inspired by classic diving watches, is the most popular first project: a rotating bezel, a bold dial with lume markers and a steel bracelet.

What comes in a dive mod kit?

A complete kit has a case with crystal and bezel, a dial, a set of hands, an NH35 movement, a bracelet or strap and the tools to assemble it. Many parts-only kits skip the movement or tools, so check before you order.

A complete dive mod

The Prodi Dive Kit · 40mm Automatic

From $349

Seven colors · NH35 automatic · tools, second dial and rubber strap included

Use code WELCOME for 10% off your order.

Choose your color

Do NH35 mod parts fit together?

Mostly yes. NH-family movements share the same footprint, dial feet positions and crown stem size, so an NH-compatible dial fits any NH movement. Cases, bezels and crystals are where sizes vary.

• Dials: 28.5 mm is the common size for NH dive builds. Match the date window to a 3 o'clock movement.
• Hands: buy hands made for NH35 posts.
• Chapter ring and bezel insert: these belong to the case design, so buy them for that case.
• Crown stem: often needs to be cut to the case, which is why a kit that pre-matches the stem saves a step.

How do you build your first dive mod?

Seat the dial, press on the hands, case the movement, then close the case and fit the bracelet. Plan on about two hours.

1. Dial onto movement. Line the two dial feet with their holes and press gently until the dial sits flat.
2. Hands. With the movement in its holder, press on the hour, minute and seconds hands in that order, each pointing at 12.
3. Into the case. Lower the movement in, slide the stem in and push the crown until it clicks.
4. Close up. Screw on the case back without over-tightening, fit the bracelet and set the time.

New to all this? Start with our guide to a watch kit for beginners, or follow the photo steps in our build guide.

Which mistakes ruin a first mod?

Mixing parts that do not match, forcing the crown stem, and touching the dial. All three are avoidable with a matched kit and a little patience.

• Buying mismatched parts. A dial for a 4 o'clock date will not line up with a 3 o'clock movement.
• Forcing the stem. If the crown will not click home, pull it out and check the angle instead of pushing harder.
• Fingerprints on the dial. Handle it by the edges with gloves or finger cots.
• Hands set at different times. Fit every hand pointing at 12, or the date will change at the wrong moment.
• Skipping the pressure test. Any home build should be tested before it goes in water.

Which movement should your mod use?

An NH35-compatible movement is fine for a first mod. The Seiko TMI NH35A suits a watch you will keep and service.

Both fit the same parts, so you can upgrade later. See the full comparison in NH35 vs NH35A.

How much does an NH35 mod cost?

Buying every part and tool separately for a first build quickly adds up, because the tools alone are a real expense. A complete kit bundles them into one price.

Our kit is $349 with the standard movement or $449 with the Japanese NH35A, with tools, a second dial and a rubber strap included. Compare that with any parts list you build yourself, and remember to price the hand presser and movement holder. More on what to compare in our guide to choosing a build your own watch kit.

What can you change after your first mod?

Dials, hands, straps and bezel inserts are the easiest upgrades. Each uses the same tools and steps you learned on the first build.

Our sunburst dial and hands fit NH35 movements, and a 20mm rubber strap is the quickest change of all.

The bottom line

An NH35 mod kit is the easiest way into watch modding: standard parts, a reliable movement and a result you can wear. Start with a complete dive mod, learn the four steps, then swap dials and bezels as your taste grows. Choose your color.