Assemble Watches
Watch Modding Glossary
Plain-English definitions for the terms you'll encounter when modding a Seiko watch. New to modding? Start with the Beginner's Guide.
- NH35
- An automatic movement manufactured by Seiko SII. It hacks (stops when the crown is pulled out), hand-winds, and runs at 21,600 bph. The most popular movement choice for Seiko mods due to its compatibility with SKX007 and SRPD case footprints, and its drop-in replacement of the older 7s26.
- NH36
- A close relative of the NH35 with an additional date function positioned at 3 o'clock (the NH35 date is at 3 o'clock too, but the NH36 adds a day display). Same footprint, same hacking and hand-winding. Choose based on whether your dial has a date window at 3 or 4.2 o'clock.
- 7s26
- The older Seiko automatic movement found in SKX007s and many other vintage Seiko models. Non-hacking, non-hand-winding, and less accurate than the NH35. Commonly replaced during a mod for the NH35 or NH36.
- SKX007
- A Seiko dive watch produced from 1996 to 2019, widely regarded as the starting point for Seiko modding. It uses a 46mm case, 22mm lug width, and a 7s26 movement. The SKX007's discontinuation triggered a wave of aftermarket compatible parts and remains the most-modded Seiko platform.
- SRPD / 5KX
- The current-production heir to the SKX007. The SRPD51, SRPD55, SRPD65, and related 5KX series watches share similar case dimensions and movement footprint with the SKX007. Most SKX-compatible aftermarket parts also fit the SRPD; always verify with the vendor.
- Fauxtina
- A portmanteau of 'faux' and 'patina'. Refers to dials (and sometimes hands) designed to mimic the aged, cream-coloured appearance of vintage watch lume, without the decades of actual ageing. Popular in vintage-inspired Seiko builds and pairs well with gold or warm-toned handsets.
- Chapter ring
- A separate ring that sits between the dial and the crystal, adding a tachymeter scale, dive graduations, or visual depth. A popular Seiko mod addition, but it adds height between the dial and crystal; always verify case depth compatibility before ordering.
- Dial feet
- Small metal tabs on the underside of a watch dial that slot into corresponding holes in the movement. The position, number, and diameter of dial feet must match your movement exactly. It's the most common compatibility check before ordering any aftermarket dial.
- Hardlex
- Seiko's proprietary mineral crystal, used in the stock SKX007 and most entry-level Seiko watches. More scratch-resistant than standard mineral glass, but not as tough as sapphire. Commonly replaced with a flat or domed sapphire crystal during a mod.
- Sapphire crystal
- A watch crystal made from synthetic corundum (sapphire). Extremely scratch-resistant, optically clear, and the most common crystal upgrade in Seiko modding. Available in flat, domed, and double-domed profiles; each looks different and requires a different installation method.
- Lug width
- The distance (in mm) between the lugs of a watch case, which determines what strap or bracelet will fit. SKX007 and most SRPD variants use a 22mm lug width. Always confirm lug width before buying straps.
- Hand tube size
- The inner diameter of a watch hand — the hollow tube that fits over the movement's stem pinion posts. Hours, minutes, and seconds hands each have different tube sizes. Tube size must match the pinion posts of the movement; mismatch is a common beginner mistake.
- Bezel insert
- The removable ring that sits inside the bezel of a watch, typically printed with a dive scale, GMT scale, or tachymeter. The insert is separate from the bezel itself and can be swapped independently. Available in aluminium, ceramic, and sapphire materials.
- Rodico
- A brand of waxy cleaning putty used by watchmakers to lift dust, fingerprints, and debris from dials and hands without scratching. Essential for any dial or hand work; one fingerprint on a dial shows up clearly under a crystal.
- Donor watch
- A watch stripped for parts to use in a mod build. The 'donor' provides the movement, case, or other components. A beater-grade SKX007 or SRPD is the most common donor for Seiko mods.
- Hacking
- A movement feature that stops the seconds hand when the crown is pulled out, allowing precise time-setting. The NH35 hacks; the older 7s26 does not. Also written as 'hand-setting' or 'hack-setting'.
- Hand-wind
- The ability to manually wind a watch's mainspring by turning the crown. The NH35 and NH36 support hand-winding; the 7s26 does not. Useful for keeping a watch running if it's been sitting unworn.
- Spring bar
- The small cylindrical pin that connects a strap or bracelet to a watch case's lugs. Removed and replaced using a spring bar tool. One of the most basic tools in any modder's kit.
- WR / water resistance
- Water resistance rating, measured in metres (e.g., 200m WR). After any caseback or crystal work, the original WR rating is no longer guaranteed. Have the watch pressure-tested by an independent watchmaker if water resistance matters to you.
- Crystal press
- A tool used to seat and remove watch crystals. Required for any crystal swap; improvising without one risks cracking the crystal or damaging the case.
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