Add 10 rounds to your Glock 9mm magazines! Machined from billet aluminum and hard anodized for durability, these extensions are tough enough for competition or carry with any Pistol Caliber Carbine. Also included is an extra power magazine spring, designed to work perfectly with factory 31 round magazines, for a total of 41 rounds! Best of all these extensions are easy to install and remove! No gunsmithing required, the built in push pin design makes installation a snap.