How Movement Choice Affects The Other Seiko Mod Parts On Your Build
A lot of Seiko modding beginners start the same way. They pick a dial they like, choose a cool set of hands, maybe grab a case that looks solid, and only think about the movement towards the end of the planning phase. Most of the time, that works especially when using an NH35 which fits almost everything. It is forgiving, widely supported, and rarely causes problems.
But the moment you step outside the standard NH35 or NH36, the movement stops being just an afterthought and something to think twice about. Thickness, hand height changes, dial layout; these can change which means some of the other parts will need to adjust. Even the crown position can sometimes become an issue.
If you choose the wrong movement without planning around it, small details can ruin an otherwise great watch. Here is how different movement choices affect the rest of your parts.
When Adding GMT
The NH34 is popular because it adds GMT functionality at a reasonable price. Being able to track a second time zone makes a build feel more advanced and sporty, but that extra GMT hand comes with trade-offs.
The biggest change is hand height. The GMT hand post adds extra thickness to the hand stack, which means your seconds hand which would normally function flawlessly on a 3-hander build can bump on the crystal when used for a GMT build. In the worst case, it can stop the hand from moving entirely, and that is no better than having a dead watch.
The solution is simple but must be planned. A double-domed crystal gives more internal clearance. Some cases are designed specifically for NH34 builds and already account for this extra height, but if you are using a case made for NH35 proportions, upgrading the crystal is strongly recommended.
Dial options also become more limited with an NH34 movement, as the center hole is slightly larger than regular NH dials, again, on account of the GMT Hand post.
Date Wheel Concerns
The NH36 doesn’t really affect a build much aside from requiring a dial with a day and date window, but you still need to make sure that your NH36 has a date wheel with the correct orientation that matches the case’s crown position.
If your case has a 3 o’clock crown, then in most cases, you’re fine as the NH36 is primarily made for these. But if you’re using a 4 o’clock-oriented case like the SKX007, then you’ll have to swap the date wheel, otherwise you’d get a subtle but annoying misalignment!
Dealing with Skeletons
With skeleton or open-heart movements like the NH70 and NH72, the movement is no longer hidden and instead becomes the main visual feature. That changes everything.
The dial must allow the movement to show through; a solid dial defeats the purpose. Most builders use skeletonized or heavily cut-out dials so the gears and balance wheel are visible. Hand selection also becomes more important. On a solid dial, contrast comes from the dial color, but on a skeleton build, the background is the movement itself. If the hands blend in with the metal plates, you get reduced visibility, so you need something with either a high contrast finish or strong lume.
A display caseback also makes sense. If the movement is meant to be seen, hiding the back feels like a waste. And since a skeleton build is one made to show off, why don’t you add more wow factor by giving it a flashy rotor?
Thin but Demanding
The Miyota 9015 is thinner than most NH movements, and makes it a good fit for more refined builds. That thinner profile sounds like an easy upgrade, but thinness changes proportions, and that can affect the entire build.
In a case designed for an NH35, the thinner Miyota movement can sit lower, creating a visible gap between the dial and crystal or worse, it can move around inside the case which absolutely nobody wants in a mechanical watch. Yes, you can prop it up with a custom, thicker spacer so you can still take advantage of the Miyota’s smoother hand sweep thanks to its higher beat rate compared to the humble NH, and for some people that alone is worth the upgrade, but you’re missing out on the reduced thickness.
In a case built specifically for the 9015, everything lines up correctly. The movement will be a snug fit, and there is no chance of the crown not aligning properly. And with small and thin watches being the current trend, you’re building something relevant and timely.
The Miyota 90S5 shares the same thickness and stem position as the 9015. That means it carries the same case compatibility requirements. On top of that, it is a skeleton movement. That means like with the NH7X movements, dial choice, hand contrast, and display casebacks all matter even more.
Wrap Up
Movement choice is not just about performance. It affects dial layout, crystal clearance, case thickness, crown alignment, hand length, and even overall proportions. Thinking about the movement early on avoids costly compatibility mistakes and unusable watches later.
Ready to pick your watch’s power source? Head over to namokiMODS for your choice of genuine NH, VK Mechaquartz, and premium Miyota movements! We also have custom rotors, day and date wheels, and more to add character to your Seiko mods.
Happy modding!