Gemtech 5.56 Etm 3-port Muzzle Brake 1/2-28 . 56 Etm Flash Hider 1/2-28 Features Unmatched Reliability In Alignment With Etm Equipped Suppressors; 2.375'' Long Pre-dimpled For Pin And Weld To 14.5'' Barrel; Virtually Eliminates The Possibility Of Carbon Locking With A Suppressor Attached. Specifications for Gemtech 5.56 Etm 3-port Muzzle Brake 1/2-28: Manufacturer: Gemtech Caliber: 5.56mm Package Contents: Gemtech 5.56 Etm 3-port Muzzle Brake 1/2-28