Plumbing fittings vary by size, purpose and material. You often must tie together pipes of different materials with transition fittings. The materials in common use today — copper, PVC and CPVC ...
the grip-style mechanical fittings (Photos 3 and 4) can be used on both copper and CPVC pipe. Don't confuse CPVC pipe with the plastic polybutylene systems that were a problem more than a decade ago.