This part of ISO 16486 specifies the physical and mechanical properties of fittings made from unplasticized polyamide (PA-U) in accordance with ISO 16486-1, intended to be buried and used for the supply of gaseous fuels. It also specifies the test parameters for the test methods to which it refers. ISO 16486 is applicable to PA-U piping systems the components of which are connected by fusion jointing and/or mechanical jointing. In addition, it lays down dimensional characteristics and requirements for the marking of fittings. In conjunction with the other parts of ISO 16486, it is applicable to PA-U fittings, their joints, to joints with components of PA-U and to joints with mechanical fittings of other materials, and to the following fitting types: — fusion fittings — electrofusion fittings and butt fusion fittings; — transition fittings.