Watch aficionados, be they watch modders or collectors, recognize that within the world of watches, Seiko Mod has surpassed the art of trend – it's a reimagining of creative craftsmanship. And out of them, the most popular engine for the majority of custom watches is the Seiko NH Movement Series.

Built for performance, renowned for their reliability, and loved for modding, these movements are the beating hearts of nearly every major Seiko Mod build in existence today.

So why are they so special? And how do you choose the best one for your custom project? Let us take a look at the NH movement family, and why TGM Watches proudly uses them in every custom build.

What is a Seiko Mod — and why does the movement matter?

Seiko Mod (Seiko Modification) is a custom-made watch employing Seiko's platform for mechanical movement. Genuine Seiko movements are used in the watches, while other features such as the dial, bezel, case, and hands are substituted or altered.

But at the heart of any great mod is the movement — the beating heart of the watch. It's what gives the timepiece accuracy, smoothness, and life. And for most modders, Seiko NH movements are the way to go.

Overview: What are NH Movements?

The Seiko NH Series is a family of mechanical automatic movements made by Seiko Instruments Inc. (SII). They evolved from the legendary 7S26 movement — bringing more features, better finishing, and higher reliability, while remaining accessible and mod-friendly.

These movements offer:

• 21,600 vibrations per hour (vph) – reliable accuracy and smooth sweep

• Hacking seconds – allows the second hand to stop when setting time

• Manual winding – hand-wind option in addition to auto winding

• High mod compatibility – fits most mod cases and aftermarket parts

Currently, there are about 10+ variations in the NH family. Let’s break down the most commonly used ones in the Seiko Mod scene.

NH36 – Day + Date for Extra Functionality

The NH36 shares the same core specs as NH35, but includes both day and date complications — making it great for builds inspired by classic diver watches or SKX-style pieces.

 Key Features:

• Same structure as NH35

• Displays day of the week + date

• Perfect for symmetrical dial layouts

• Same dimensions, same reliability

We use the NH36 in pieces like the all-black TGM I 106S and the bold gold-accented TGM I 06R I — both of which demand functional elegance with daily wear usability.

NH38 / NH39 / NH70 – For Open Heart & Skeleton Lovers

If you want to build something visually dramatic, these are your movements.

• NH38 – No date, open heart at 9 o’clock. Clean and modern.

• NH39 – Open heart + 24-hour subdial at 6 o’clock. Adds depth and symmetry.

• NH70 – Full skeleton design. All gears exposed. Perfect for technical and artistic builds.

These movements are slightly more niche but offer maximum impact for custom designs.

At TGM, we’re developing a new line of skeleton Seiko Mods powered by NH70 to be released in 2025 — stay tuned.

 Why TGM Watches Only Uses Genuine Seiko Movements

We don’t compromise on core components. Every TGM Mod is powered by authentic Seiko NH movements from certified sources.

Here’s why:

• Precision & durability tested across years

• Easy servicing – parts are widely available worldwide

• Perfect compatibility with modding components

• Feels smooth, winds easily, and performs consistently

You can tell the difference the moment you wind it — the rotor sound, the glide of the second hand, and the flawless integration with the case. That’s the Seiko difference.

How to Choose the Right NH Movement for Your Seiko Mod

Seiko Mod Isn't Complete Without the Right Heart

Your custom build is only as good as what beats inside it. Whether you’re starting your mod journey or planning your next masterpiece, choosing the right NH movement is where it all begins.

At TGM Watches, we’re proud to assemble all our Seiko Mods by hand, using only the best parts — starting with what matters most: the movement.

Explore Our NH-Based Custom Builds📦 Worldwide shipping | 12-month warranty | Hand-assembled