YHM's Low Profile Flash Hiders offer the same great performance as their Phantom Flash Hiders, eliminating 99% of the visible muzzle flash. Their low profile design allows a gas block with an inside diameter of 0.75"" to be installed and uninstalled without the removal of the Flash Hider. SPECIFICATIONS Caliber = 5.56mm/.223 Diameter = 0.735" Length = 2.225" Weight = 1.8 oz. Thread Pitch = 1/2" x 28 Finish = Melonite QPQ Includes Low Profile Crush Washer (YHM-24-W) Mfg: Yankee Hill Machine Co., Inc.