Follow the links. For the Micri Roni, you'll see you have to order different models depending on the Glock frame size. For the MCK, it's one size fits all. Except for the G21 frame.
https://www.opticsplanet.com/comman...ersion-w-stability-brace-for-glock-17-22.html
https://www.opticsplanet.com/caa-glock-mck-micro-conversion-kit.html
This is true for the Gen 3 but the Gen 4 will accept both the Compact and Full size Glocks in 9, 40 and 357 sig. There is an adjustment on the muzzle shroud.