The Apollo Expansion PEX Brass PEX-A Barb to Polybutylene Coupling is simple to install and designed for the transition from polybutylene pipe to PEX-A tubing. Apollo Expansion PEX transition couplings must be secured into place Apollo Expansion PEX sleeves or comparable expansion-type sleeve or ring (all sold separately). The Apollo Expansion PEX system is a comprehensive cold expansion piping system comprised of brass fittings, poly alloy fittings, manifolds, valves, fasteners, tools and tubing designed for implementation in water delivery systems, simple or complex. A cold-expansion tool (sold separately) is required for installation.