The Gen 2 Micro Bastard Self Timing Muzzle Brake is a stainless steel AR-15 muzzle device featuring a self-timing design with an installation nut for at-home installation. No crush washers or peel washers are required. Available in Stainless (G2M9630S) and nitrided variants with 9/16x24 or 1/2x28 threads. Specifications: Caliber .308, inner diameter 0.75 in, outer diameter 0.75 in, length 1.86 in, weight 1.8 oz, country of origin USA. Package contents: American Precision Arms Micro Bastard Self Timing Muzzle Brake.