This part of ISO 8283 specifies the design formulae and the derived dimensions, together with tolerances, of sockets and spigots for joints of polypropylene (PP) fittings and for integral sockets of PP pipes used in discharge systems inside buildings where such joints are intended to accommodate expansion and contraction in the discharge system. NOTE 1 Polypropylene means plastics based on polymers of propylene or copolymers of propylene with other monomers, the propylene being in the greatest amount by mass. (Definition based on that given in ISO 472:1988, Plastics — Vocabulary.)