Will any keycap set fit my mechanical keyboard?

If your switches are standard MX-style and your layout is 60%, TKL or full-size — yes. Otherwise check three things: stem type, profile row heights vs your layout, and set key sizes (1.75u Shift, arrows, numpad kits).

Do Cherry profile keycaps work on OEM boards?

Yes — Cherry and OEM are both MX-stem compatible sculpted profiles; the difference is shape and feel, not mount. Sculpted profiles only become an issue on non-standard layouts needing row kits.

Are Hall Effect switches compatible with normal keycaps?

Mostly yes — HE stems are MX-style. But tolerance variations can make tight SA/MT3 skirts pop off, box-style stems can bind very tight caps, and low-profile HE switches need LP cap sets.

Keycap compatibility: the complete rulebook

Whether a keycap set works is three separate questions: stem mount, profile vs layout, and key sizes included. Fail any one and the set doesn't work.

Rule 1 — Stem mount (the hard gate)

Switch stem	Keycap it takes	Gotchas
Cherry MX cross (~4.1 mm)	Anything labeled "MX compatible" — Cherry, OEM, SA, DSA, XDA, MT3, KAT, KAM…	The default; 95% of the market.
Kailh Choc (low profile)	Dedicated Choc sets (few!).	Standard MX caps sit wrong/loose; even generic "low-profile MX" caps don't fit Choc's smaller cross.
Low-profile MX-style (Keychron LP, NuPhy, Lofree)	LP keycap sets for that board family.	Normal MX caps are too tall — they hit the deck.
Topre (capacitive)	Topre mounts or sliders (Realforce/HHKB/Nova).	Completely different ecosystem; MX via sliders only.
Alps / Matias	Alps-mount vintage or Matias sets.	Legacy; niche.
Hall Effect magnetic	MX-profile sets, with fit-tolerance checks.	Tight SA/MT3 skirts may pop off narrow stems; box-style stems (e.g. Magnetic Jade Gaming) can bind very tight caps; LP-HE needs LP caps. HE details →

Rule 2 — Profile × layout (the row-kit gate)

Sculpted profiles (Cherry, OEM, SA) have row-specific heights — R1 bottom row through R4 number row. On standard layouts the set is pre-arranged; on non-standard layouts you need matching kits:

Layout	Cherry / OEM / SA (sculpted)	DSA / XDA / KAT / KAM / MT3 (uniform)
60% / TKL / full	✅ standard sets cover it	✅ always
65% / 75% / 96%	⚠️ verify kit has 1.75u Shift, arrows, extra column (65); F-row kit (75); nav + numpad kits (96)	✅ usually one kit covers all — verify key count
40%	⚠️ needs dedicated 1u row kits, often sold separately	✅ ideal
Alice / arched	⚠️ needs a mirrored Alice kit or rows look inverted on the right half	✅ sidesteps the issue entirely
Split / ortho	⚠️ needs ortho kits with 1u everywhere	✅ purpose-built for these
Low-profile boards	⚠️ use LP cap sets; tall profiles won't clear the case (SA especially)

Uniform profiles are also the safe pick for columnar boards (ErgoDox, Lily58) and Mac-specific bottom rows, because nothing depends on row position.

Rule 3 — Key sizes included (the kit-list gate)

Sculpted or not, check the kit list for what your board needs:

65%: 1.75u right Shift, 1u arrows, extra right column, often split Backspace/1.75u? check.
75% / 96%: 1u F-row keys, nav column, numpad kit (96%).
Split spacebars (7u? 6.25u? 6.5u?): boards with split space or unusual bottom rows need those specific widths — 6.25u is the ANSI default, 6.5u common on Winkeyless, 7u on many customs.
ISO / UK: needs ISO Enter, tall Backslash, short Left Shift — most "full kits" include them; cheap base kits don't.
Mac: 1.25u bottom-row Option/Command layouts — usually covered, verify.
40%: extra 1u number-row-height keys (R1) and often a dedicated "40s kit".

Quick answers

"Are Cherry profile caps compatible with my OEM board?" Yes — both mount on MX stems; profile only changes feel.
"Will SA caps fit my low-profile board?" No — LP boards need LP cap sets (and SA would brush the case anyway).
"Do XDA caps work on my 40%?" Yes, perfectly — uniform profiles don't care about rows.
"My caps pop off my magnetic switches." HE stem tolerance — try a cap with a thinner skirt wall, or a different HE switch with a standard MX stem. More →
"The legends don't line up on my Alice." Sculpted profile without the mirrored Alice kit — switch to a uniform profile or buy the Alice kit.