How do I measure lug width?

Measure the distance between the two lugs in millimetres, at the point where the strap meets the case. A cheap ruler works; a caliper is better. Or search your watch model in this guide's table.

Which G-Shock models need an adapter?

The GA-2100 (CasiOak), the DW-5600 square family and the F-91W all use proprietary mounts - an adapter converts them to standard spring-bar widths. The MDV-106 Duro takes 22mm straps directly with no adapter.

Are GA-2100 and AE-1200 parts interchangeable?

No. GA-2100 cases, straps and adapters do not fit the AE-1200 (Royale) and vice versa. Always check the fitment line on the product page.

Do Apple Watch bands need an adapter?

No. Apple Watch uses a slide-in band slot - pick the band matched to your case size (38-41mm small, 42-49mm large).

MODDING 101 — GUIDE 02

Strap Width & Adapter Guide — Every Watch Line We Support

One table, zero guesswork. Find your watch, read its lug mount, see whether you need an adapter – then shop the matching collection.

The quick-answer table

Watch	Lug mount	Adapter?	Strap width
GA-2100 / 2110 / B2100 (CasiOak)	Proprietary resin mount	Required	22mm via adapter (16-20mm variants exist)
DW-5600 / 5610 / GW-M5610 (Square)	Proprietary square mount	Required	16mm stock; adapters open standard widths
AE-1200 / AE-1300 (Royale)	Proprietary	Per product	16-22mm depending on case
F-91W / A158 / A159	Standard 18mm spring bars	No	18mm direct
MDV-106 / 107 (Duro)	Standard 22mm	No	22mm direct
Seiko 5 / SKX builds	Drill-lug (case dependent)	No	22mm typical
Apple Watch (38-49mm)	Band slide slot	No – size-matched band	Per case size

Line by line notes

CasiOak (GA-2100 family)

The mod scene’s favourite. The stock resin band needs a bracket adapter – once fitted, any two-piece 22mm strap drops on. Metal cases replace the resin shell entirely and expose standard bars, so straps go direct.

G-Shock Square (DW-5600 family)

Same story as the CasiOak: proprietary mount, adapter unlocks it. Square mods shine with steel bracelets and leather – widths beyond the stock 16mm open up with the right bracket.

Casio Royale (AE-1200 / AE-1300)

The budget mod hero. Stock bands are 16mm; metal cases move the goalposts, so check the specific case listing. Our AE-1200 adapters and cases state the resulting width on every page.

F-91W

The cheapest full mod platform there is: 18mm, direct swap, no adapter. Metal case kits bundle the hardware.

Duro (MDV-106)

The giant that takes 22mm like a standard watch. Dive bracelets, rubber, sailcloth – all direct-fit.

Apple Watch

No lug drama: buy the band sized for your case. Our carbon Apple Watch kits list the compatible case size in the title.

How to measure lug width in 30 seconds

Take the strap off, or measure between the two lugs where the strap meets the case.
Millimetres only. A 20mm strap never fits a 22mm lug – there is no “close enough”.
Odd number? You likely measured the strap, not the gap. Re-measure lug to lug.

Shop by line

GA-2100 parts · Adapters · Square parts · AE-1200 parts · F-91W parts · Duro straps · Apple Watch bands