1.1 This specification covers metal insert fittings and copper crimp rings for use with cross-linked polyethylene (PEX) tubing in 3/8, ½, 5/8This specification covers metal insert fittings and copper crimp rings for use with SDR9 cross-linked polyethylene (PEX) tubing. All performance tests shall be performed on assemblies of fittings, crimp rings, and PEX tubing. Fittings and crimp rings s