Pex crimping system is among the oldest, most reliable and most widely used methods of installing PEX. Copper crimp rings ensure full 360˚ compression of the pipe over the barbs of the fitting without the risk of expansion or corrosion. Size of the PEX crimp ring corresponds to the PEX pipe size, namely, 1/2 inch crimp rings for 1/2 inch PEX, 3/4 inch for 3/4 inch and so on. A PEX crimp ring is installed by positioning it over the pipe and fittings and compressing it with the help of a PEX crimp (crimping) tool. ⚠ California Proposition 65 Warning: This product is known to the state of California to cause cancer, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.