Glock plus 2 magazine extensions fits all double stack Glock 9mm, .40 and .357SIG. Will not fit single stack mags like the Glock 42 and 43.
This is the complete kit. Includes new plus 2 extended baseplate and plus 2 mag insert. Many shops just sell the baseplates; this will only work reliably with both the baseplate and insert used together.
Glock plus 2 extensions add 2 rounds to 9mm magazines and 1 round to .40 and .357 SIG magazines.