Movement, case, dial — parts that fit together.

The single biggest cause of stalled first builds isn't bad technique — it's parts ordered separately that don't actually fit together. This is the compatibility cheat sheet nobody seems to publish in one place.

The five dimensions that have to match

For a watch build to come together cleanly, five dimensions have to align across your movement, dial, hands, case, and bracelet:

• Movement family — determines dial foot positions and hand sizes
• Dial diameter — must match the case's dial opening
• Dial foot positions — must align with holes in the movement plate
• Hand fitting sizes — must match the movement's pinion sizes
• Lug width — must match the bracelet or strap

Get any of these wrong and the build doesn't complete. Get all five right and assembly becomes the fun part.

1. The movement family is the foundation

Every other compatibility decision in a build flows from the movement you choose. The Seiko NH35, NH36, and NH38 share identical dimensions — a dial designed for one fits all three. The NH05 has slightly different dial-foot positions and is sold separately. The NH70 (skeleton) shares the same diameter and height as the NH35/36/38 but uses skeleton-specific dials.

Notice the hand sizes are identical across all five calibres. This is deliberate — Seiko engineers wanted parts cross-compatibility within the NH family. The dial foot positions are different between the NH35-series and the NH05, however, which means an NH35-cut dial will not fit an NH05 movement and vice versa.

2. The dial diameter must match the case

The most common dial size for NH-series builds is 28.5mm — this is what fits 38mm to 42mm cases designed for the family. Smaller cases (36mm, 34mm) use proportionally smaller dials (usually 27.5mm or 26.5mm). Larger cases (44mm+) use 31mm dials.

The dial must sit cleanly inside the case's dial opening with no visible gap and no overhang. Order a 28.5mm dial for a case designed for 27.5mm dials and you'll have a dial that doesn't fit. Order a 27.5mm dial for a 28.5mm case and you'll have a visible ring of empty space around the dial when you look down at it.

Modern modding cases almost always specify their dial diameter explicitly. If a case listing doesn't tell you, don't buy it.

3. Dial foot positions are the trickiest part

The dial has three small posts protruding from its underside. The movement has three corresponding holes. The posts slot into the holes and friction holds the dial in place. The positions of these posts vary between movement families.

On an NH35, the three dial feet sit at 11:00, 5:00, and 7:00 positions relative to the movement's centre (using a clock-face analogy). On an NH05, the positions are shifted — typically 12:00, 4:30, and 7:30. This means a dial cut for one will not fit on the other without rebending the feet or drilling new holes (both bad ideas).

The good news: most aftermarket dials are cut for the NH35 family because it's the most-modded movement. The NH05-specific dial selection is smaller. The NH70-specific dial selection (skeleton dials) is smaller still. If you want a maximum-choice dial library, build on NH35. If you have a specific dial in mind, check which movement it's cut for before you buy.

4. Hand sizes must match the movement

Watch hands are described by three numbers — the hour-hand bore, the minute-hand bore, and the seconds-hand bore. For NH-series movements, the standard sizing is:

You'll see this written as "1.50/0.90/0.20" on hand listings. If you see "1.20/0.70/0.20" or any other combination, those hands are for a different movement family — most commonly the smaller Miyota 9015 or the various ETA calibres. They will not fit an NH-series watch.

Hand height matters too — particularly the hour hand. Some hour hands are designed for thicker dials and sit too high above the movement, leaving the minute hand too far above the dial. This is rare with hands sold for the NH series but worth checking if you're buying from a non-standard supplier.

5. Lug width must match the bracelet

The lug width is the distance between the two lugs on either side of the case where the bracelet attaches. It's measured in millimetres. A 20mm lug width takes a 20mm bracelet or strap, and absolutely nothing else.

Most NH35-compatible cases come in 20mm or 22mm lug width. Some smaller cases (designed for 36mm overall) come in 18mm. Larger pilot-style cases come in 22mm or 24mm.

If you're swapping a strap on an existing watch, lug width is the only number you need to know. Measure it with calipers or check the manufacturer's spec sheet. Order the matching strap. Done.

Other compatibility considerations

Crown and stem

Most NH-series cases come with their own crown and stem, sized for that case. If you're sourcing them separately, the stem must be a standard 0.90mm diameter at the movement-side end. The crown must be threaded to fit the stem. Mixing components from different suppliers can introduce fit problems — buy crown and stem from the case maker if possible.

Crystal

The crystal is usually integrated with the case (pre-fitted at the factory). If you're sourcing a separate crystal, it must match the case's crystal diameter and have appropriate gasket sizing for waterproofness.

Caseback

Casebacks are case-specific. A solid steel screw-down caseback for one case may not thread into another. Always source the caseback with the case.

Movement holder / clip

Most NH-compatible cases include a movement ring (a plastic spacer that centres the movement inside the case). If your case doesn't come with one, you may need to source it separately or 3D-print one. Without it, the movement rattles inside the case.

The Seiko SKX/SRPD compatibility ecosystem

A huge proportion of the modding aftermarket designs to a single specification — the Seiko SKX007 (discontinued 2019) and its successor the SRPD61. These watches use:

If you're sourcing parts and you see them described as "SKX-compatible" or "SRPD-compatible", they fit the spec above. This is the most reliable signal in the modding world. A dial labelled "fits SKX" will work in any case that's also labelled "fits SKX".

The cheat sheet

If you're sourcing parts for a build from scratch and you're nervous about compatibility, follow this rule: pick the case first. Cases are the most variable component and have the most fit-specific requirements. Once you've chosen a case, every other component should be listed by the supplier as "fits this case" or "fits NH35 + 28.5mm dials + 1.50/0.90/0.20 hands + [lug width]mm strap".

If a part listing doesn't tell you the specifications, don't buy it. The reputable modding suppliers (NamokiMODS, DLW Watches, Crystal Times, Lucius Atelier) list compatibility explicitly. The unreliable ones — random Etsy sellers, AliExpress unbranded listings — often don't.

What we do at the bench

The Modding Bench's parts library is sized to a known compatibility set. Every dial in our library fits every case in our library. Every hand set fits every movement we offer. The student doesn't have to worry about specifications — they pick on aesthetics, not on engineering. We've already done the compatibility work upstream.

If you're trying to build at home and you're paralysed by spec-sheet anxiety, this is one of the bigger reasons to use a class for your first build. After you've assembled one watch under guidance, the compatibility logic becomes second nature, and you can source parts confidently for the next.