Start with the electrical system
MX mechanical contact switches, low-profile mechanical families and Hall-effect magnetic switches are not interchangeable categories. Firmware and sensing hardware matter before stem shape.
Then inspect physical retention
Three-pin and five-pin describe locating legs in addition to electrical pins, but the exact PCB holes, hot-swap socket, plate opening and housing clearance decide fit. Verify the keyboard documentation.
Avoid irreversible default advice
Clipping plastic locating legs may make some five-pin housings fit a three-pin PCB, but it is irreversible and does not solve other incompatibilities. The fit checker reports the question rather than instructing modification.