OPS Inc muzzle brake kit for the 12th model suppressor 22/.223/5.56mm includes muzzle brake, barrel sleeve with set screw, crush washer, and thread protector for outer threads that suppressor uses and instructions. Requires the use of Rocksett (NOT included) Same system used on U.S. military Mk-12 SPR rifles Stainless steel construction Matte black finish Mfg: Ops Inc SPECS: Steel construction, matte black finish. 223 - A 1/2-28 threads.