SilencerCo Low Profile 3-Lug Mount, 45 ACP AC2448 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.