Ruger Radial Ported Muzzle Brake 35 Cal Black Oxide Steel. Made from 4140 chrome molly steel with a black oxide finish to complement most firearms. Installs with an open end wrench or crescent wrench. Torque the brake to 15-20 ft-lbs. - no crush washers are required. It fits rifles with " x 28 threads chambered in .350 Legend including the AR-556 MPR and the Ruger American Rifle Ranch and the PC Carbine chambered in 9mm. Specifications for Ruger 90699 Radial Ported Muzzle Brake 35 Cal Black Oxide Steel: Manufacturer: Ruger Finish: Black Oxide Fabric/Material: Steel