This part of ISO 14531 specifies the physical properties and mechanical-performance requirements for full-end-load-resistant mechanical fittings for use in the connection of crosslinked polyethylene (PE-X) pipes conforming to ISO 14531-1 and in the construction of transition assemblies for joining PE-X pipes to metal pipes having plain spigot, screw thread, compression socket and flange terminations. In addition, it lays down dimensional requirements and specifies some general material properties (including chemical resistance) together with a classification scheme for PE-X fitting materials produced in the form of pipe. This part of ISO 14531, when used in conjunction with the other parts of ISO 14531, provides the basis for the design, manufacture and installation of PE-X piping systems (PE-X pipes, PE-X fusion fittings and mechanical fittings) for the supply of category D and category E hydrocarbon-based fuels (see ISO 13623) at a) maximum operating pressures (MOPs) up to and including 16 bar1) and b) a maximum operating temperature of +60 °C and c) a minimum operating temperature of 1) -50 °C; 2) -35 °C; 3) -20 °C. Conformity to this part of ISO 14531-3 of mechanical fittings produced in accordance with ISO 10838-1, ISO 10838-2 or ISO 10838-3 may be claimed subject to the satisfactory conclusion of the tests listed in 5.6 and an end-use restriction on operating temperatures to the temperature range -20 °C to +40 °C. NOTE It is recognized that mechanical fittings conforming to ISO 10838-1, ISO 10838-2 or ISO 10838-3 are limited to a maximum operating temperature of 40 °C. Provision is made in ISO 14531-4 for the use on a restricted-temperature basis of ISO 10838 fittings conforming to 5.6 in conjunction with PE-X pipes conforming to ISO 14531-1. The fitting manufacturer's technical file should also be consulted for relevant supporting information.