The Pearce Grip Extension for Glock Full Metal 9+3/40+2 unit adds capacity to Mid and Full Size Glock high capacity magazines. This magazine extension replaces the original floor plate and internal locking plate and adds two rounds to a 9mm; two rounds to a 40SW and 357SIG, and one round to a 45GAP magazin.e Alters the capacity of High Capacity Full Metal Lined Glock magazines. Adds three rounds to the 9mm, two rounds to the 40SW and 357SIG and one round to the 45GAP models. Made from High Impact Polymer and withstand drop tests at temperatures from -20 F to 350 F.