The Brownells Short Muzzle Brakes offer an effective braking solution, with minimal added length Features: Designed to provide maximum braking ability in the smallest size possible One inch overall length Two rows of 0.125" ports evenly distribute exiting gasses and pressure Wrench flats on each side for simple installation Available in tool steel with a black oxide finish or stainless steel Available with a 0.75" OD for perfect fitting to AR-15 or precision rifle barrels 0.75" OD models feature A 1/2-28 threads Mfg: Brownells Construction, tool steel with a black oxide finish or stainless steel. Length - 1". Diameter - 0.75". Threads - A 1/2-28. Do not use bullets larger in diameter than .223/5.56 in SMB 5.56