The Real Avid Lug-Lok Upper Vise Block offers a revolutionary new way to safely secure your AR15's upper receiver while you work on your firearm. This non-marring, 7075-T6 aircraft-grade aluminum block slides into your .223/5.56 AR15's upper receiver and into the barrel's star chamber. There, using the Lock Knock, it locks in place while utilizing the strength of the barrel lugs. Its adjustable stainless steel vice pins hold the block at the perfect working angle. All in all, the Real Avid Lug-Lok AR15 upper vise block keeps your upper receiver out of jaws of your vice, and it allows you to properly torque your gun's barrel nuts and muzzle brakes without damage to the upper receiver.