The Magpul PMAG 21 GL9 is a 21-round Glock(R) 9mm pattern magazine featuring all-polymer construction for flawless reliability and durability over thousands of rounds. The PMAG 21 GL9 is compatible with all full-size, compact, and sub-compact double-stack GLOCK 9mm variants with some protrusion below the grip. Features: Capacity: 21 rounds Caliber: 9mm Compatibility: Glock(R) pistols, Angstadt Arms UDP-9 and MDP-9 firearms This product is not manufactured, authorized, endorsed, or warranted by GLOCK. GLOCK does not warrant or represent that this product is compatible with GLOCK pistols.