The IMI Defense AR15 Lower Receiver Vice Block allows you to firmly clamp a M16/AR15 receiver halve in a vise without risk of crushing, twisting, or otherwise distorting it when applying vise pressure or torquing the barrel nut. Keeps your rifle secure for safe, effective cleaning, assembly, and repair. Torque generated while tightening the barrel nut is transmitted to the block and insert, not the receiver. The magazine catch locks to the block, safely and securely. Minimizes the possibility of damage. Holds securely without marring the finish.