The 3-Lug Mount is a quick-attach mounting option for guns with fixed barrels. The 3-Lug Mount must be used with a 3-Lug Muzzle Device. The 45 caliber 3-Lug Mount must be used only with 45 caliber 3-Lug Mount Muzzle Devices; the 9mm must only be used with 9mm 3-Lug Devices. Our 45 caliber 3-Lug Mounts are made to B&T Spec.