This muzzle brake adapter is required for use with the Barrett AM338 adapter mount suppressor. It is made of hardened carbon steel and has .75x24 threads. The adaptor is not rated for full auto fire. Barrett believes in thinking outside the box and exploring ways to improve. They are a leading manufacturer of superbly accurate long range large caliber rifles and the accessories to support them. - Required for use with AM338 adapter mount suppressor - Steel - .75x24 thread - Not rated for full auto - Black