- The Breakthrough Clean Technologies® AR15 Upper Vise Block is engineered to seamlessly fit into the barrel lugs, providing a secure anchor for vise clamping. This ensures the safe application of torque for precise manipulation of the barrel nut or muzzle device, safeguarding the integrity of the receiver. The included removable plug adds an extra layer of stability, ensuring the vice block stays firmly in place throughout use. Trust in this meticulously designed tool for worry-free and effective upper assembly work.