Pearce Grip's Magazine Extension adds capacity to Mid and Full Size Glock high capacity magazines. It 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 magazine.This 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 40 SW and 357 SIG, and one round to a 45 GAP magazine. Features: These units alter the capacity of high capacity full metal lined Glock magazines These units add 3 rounds to the 9mm, 2 rounds to the 40 SW and 357 SIG and 1 round to the 45 GAP models They are made from high impact polymer and withstand drop tests at temperatures from -20 to 350 deg F