The Ruger Radial Port Muzzle Brake design reduces felt recoil and muzzle movement. It is made from alloy steel with a black oxide finish to complement most firearms. Installs with a 11/16" open end wrench or crescent wrench. Torque the brake to 15-20 ft-lbs. - no crush washers are required. This brake is compatible with AR-556 rifles and other .223 Rem / 5.56 NATO caliber firearms with A 1/2"-28 muzzle threads.