ISO 22621 specifies the physical and mechanical properties of fittings made from polyamide (PA) in accordance with ISO 22621-1, intended to be buried and used for the supply of gaseous fuels at maximum operating pressures (MOP) up to and including 2 MPa (20 bar). It also specifies the test parameters for the test methods to which it refers. In addition, it lays down dimensional characteristics and requirements for the marking of fittings. In conjunction with the other parts of ISO 22621, it is applicable to PA fittings, their joints, to joints with components of PA and to joints with mechanical fittings of other materials, and to the following fitting types: fusion fittings (electrofusion and butt fusion fittings); transition fittings.