Locking down a new barrel? It's critical to not distort or damage the upper receiver when you're doing work like installing a barrel or torqueing a barrel nut, and the Creative Arms AR-15 Composite Vise Block makes it easy to perform any kind of torqueing operation on your rifle without fear of damaging your upper receiver. Each Creative Arms AR-15 Composite Vise Block is machined from HDPE and allows AR owners to clamp their receivers into a vise firmly and securely without placing pressure on any sensitive parts of the receiver. Simply insert the block into the magazine well, then clamp the other end of the block into your bench vise.