This is a Yankee Hill Machine Co Flash Hider known as the Phantom chambered in 308 Winchester, model YHM-3080-5C2.
5 Port Phantom design and performance in a .308 format. Includes Crush Washer. This 5 port design has no downward facing port which helps prevent dust problems when shooting in the prone position.
Features:
5/8X24 thread pitch
2.25 long;Includes crush washer;With teeth