Add 6 rounds to your G17 magazines, 5 rounds to your G22! Machined from billet aluminum, this magazine extension is engineered to add 6 extra rounds to the standard Glock 17 magazine or 5 extra rounds to the Glock 22 magazine. It comes with a special, extra power spring that is designed to handle the extra rounds. Simply replace your factory magazine extension This extension is used by top competition shooters nationwide and works flawlessly. Please Note: Does NOT work on 10 round magazines.