This extension replaces the magazine floor plate adding 1" in grip length to Glock factory 20/21/29/40 and 41 magazines. This does not alter the capacity of the magazine. This unit works on all 10mm and 45ACP Magazines except 10 round Glock 30 magazines.Features :Fits GLOCK 20/21/29/40/41/30 MagazinesWill Not Fit GLOCK 30 10 Round MagazinesMade from High Impact PolymerCompatible with Gen 3, 4, and 5 Magazines