G36C 9' .300 Black out complete assembly, gas block, op/rod spring set gas piston, barrel nut and handgaurd with rail kit and handstop. these a nitride coated inside and out, in 8 twist Threaded in the standard 5/8x 24 thread pitch. These will cycle with supers and subs and is suppressor compatible, most subs will require a suppressor to cycle properly.