Covers fittings suitable for use as fixed joints with polybutylene pipes and classified, in the case of insert fittings, according to the pressure class of pipe with which they will be used. Other types of fittings are classified according to the maximum pressure class for which they are suitable. Test requirements are specified for long-term performance, resistance to leakage when subjected to bending, resistance to pullout, liquid infiltration, thermal and pressure cycling and porosity.