PEX A Expansion Plug Poly Alloy. Barb connection. Used to permanently or temporarily cap off the ends of the PEX tubing for purposes such as pressure testing. They can also be used to prevent dirt, dust and debris from entering the open ends of PEX tubing during construction. For use with cold expansion PEX A pipe and sleeve system. Campatible with Uponor (Wirsbo) ProPEX piping systems (ProPEX is a trademark of Uponor). ASTM F1960.