Copper Crimp Rings are used to properly tighten a PEX fitting to a PEX pipe. PEX Crimping is amongst the most popular used connections today, due to its reliability. Crimp Rings form a 360 degree compression on the fitting to ensure that the pipe and fitting are securely tightened. The size of the Crimp Ring corresponds to the size of the PEX Pipe equally. You will need a Crimp tool to make any connections.