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Keycap compatibility

Please note that the following tables are concerned with mounting fit. Owing to differing stem lengths within keycaps, keycaps from another switch family may not sit at the same height above the switch as the original keycaps. So long as the keycap can be pressed down a long way onto the slider, and it cannot be pulled off with too little effort, the keycap and switch are considered compatible.

Where compatibility depends on orientation, this is noted; otherwise, keycaps that fit, do so in both orientations.

Cruciform mounts

Switch →
Keycap:
SMK 1G
upright
SMK 1G
angled
Futaba 1G complicated Futaba 1G simplified Alps SKCCAF Sasse A MEI Cherry M5
upright cross
Cherry M6
upright bar
Cherry M6
upright tee
Cherry M9
angled
Cherry M8
open top
Cherry MX
Futaba 1G simplified (Comptec) No No Yes (very tight) Yes No Yes (a bit loose) Yes No Yes No (too loose) Yes No No
SMK 1G angled (Comptec) Yes (very tight) Yes (very tight) Yes Yes (90°/270° is loose fit) No No (too loose) Yes No Yes Yes Loose fit No No
SMK 1G upright (SMK) Yes Yes Yes Yes No Yes (a bit loose) Yes (a bit loose) No Yes Loose fit Yes No No
Cherry MX (Filco) No No No No No No No No No No Yes (90°/270° only) Yes (0°/180° only) Yes (0°/180° only)
Cherry MX (GMK) No No No No No Yes (not fully) No No No No Yes Yes Yes
Mitsumi hybrid (Commodore 64) No No No (falls off) No (falls off) Yes No (stem out of reach) Yes Yes No (falls off) No (falls off) No (falls off) No (stem out of reach) No (falls off)
Tokai MM9-2 clone relegendable Yes (0°/180° is loose fit) Yes (90°/270° is too loose) Yes Yes (90°/270° is loose fit) Yes (90°/270° only) Yes (loose fit) Yes (loose fit) Yes No (falls off) No (falls off) Yes (0°/180° falls off) No No

Notes

Sources

Square post mounts

Often referred to as “RAFI mount”, this is a series of visually similar but not fully mutually compatible mounts.

Switch →
Keycap:
RAFI RS 74 M Siemens STB 11 Siemens STB 21 2.5 mm Sasse A
RAFI RS 74 M Yes Yes (a bit loose) Yes (loose fit) No
Sasse A (AliExpress) No (too loose) Yes (loose fit) No (too loose) Yes

Unfortunately my collection of both switches and keycaps is very limited at present; I do not have RS 76 switches or keycaps, nor any Siemens keycaps. I also have no guarantee that the keycaps that came with my Sasse switches are original Sasse parts, although they are the correct design.