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 40SW and 357SIG, and one round to a 45GAP magazine. These units alter the capacity of High Capacity Full Metal Lined Glock magazines. These units add three rounds to the 9mm, two rounds to the 40SW and 357SIG and one round to the 45GAP models. They are made from High Impact Polymer and withstand drop tests at temperatures from -20 F to 350 F. DISCLAIMER: GLOCK is a federally registered trademark of GLOCK, Inc. and is one of many trademarks owned by GLOCK, Inc. or GLOCK Ges.mbH. Neither Sportsmans Outdoor Superstore nor this site are affiliated in any manner with, or otherwise endorsed by, GLOCK, Inc. or GLOCK Ges.mbH. The use of GLOCK on this page is merely to advertise the sale of GLOCK pistols, parts, or components. For genuine GLOCK, Inc. and GLOCK Ges.mbH products and parts visit www.glock.com.