28 mm straight coupler. Polyplumb is the fast and permanent grey plastic pushfit system for domestic hot and cold water supply, radiator and floor heating installations. Fittings feature stainless steel grab ring and are demountable by disassembling, reducing the potential for tampering. Pipe stiffeners must be used when using plastic pipe ; these are not required for copper pipe. Manufactured by a BS EN ISO 9002:2008 registered company. Polyplumb polybutylene barrier pipe, fittings and accessories are Class S rated to BS 7291-1, covered by BBA Certificate No. 00/3699 and Kitemarked to BS 7291-1 and 2. Polyplumb is listed in the WRAS Water Fitting and Materials Directory. Polyplumb must not be used for gas, oil, compressed air, solar heating, primary or gravity pipework from a solid fuel back boiler.