The 3-Lug Mount is a quick-attach mounting option for guns with fixed barrels. These 3-lug muzzle devices require a 3-lug mount to attach a suppressor. The .45 caliber 3-lug muzzle devices must be used only with 45 caliber 3-Lug Mounts. The 9mm 3-lug muzzle devices must only be used with 9mm 3-lug mounts.