The shield arms glock 19/23 magazine extension adds 5 rounds to your glock 19 magazine, and 4 rounds to your glock 23 magazine.Shield arm's unique, easy access floor plate design allows you to quickly access the spring and follower without having to remove the extension from the magazine body.Caliber: 9mm LugerCapacity: 5rdFinish: AnodizedModel: Magazine ExtensionMaterial: AluminumCapacity: 5