A 5.56mm/.223 Caliber Muzzle Brake - production approved by the BATF - featuring four gas ports and a ribbed design to improve cooling. Machined of 4140 gun steel with a manganese phosphate finish - very effective in controlling muzzle rise. Slip-on/taper pinned version for barrels with plain crowned muzzles, and threaded model (shown left - threaded 1/2" x 28 T.p.I.) can be installed without regard to port location (timing) and will still be effective, however most are installed with ports positioned 12 - 3 - 6 - 9 o'clock. The slip-on, pinned version requires factoryinstallation or professional gunsmithing to drill and install the taper pin, andfor extra safety,highstrength Loctite should be used in addition to the taper pin. Bushmaster Izzy Brake for threaded barrels - requires lock washer.