This muzzle brake adapter is required for use with the Barrett AM338 adapter mount suppressor. It is made of hardened carbon steel and has .75×24 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 – .75×24 thread – Not rated for full auto – Black