This document 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. NOTE Additional information about the suitability of PA-U pipe systems for hydrogen and its admixtures is given in ISO 16486-1:2023, Annex D. It also specifies the test parameters for the test methods to which it refers. The ISO 16486 series is applicable to PA-U piping systems, the components of which are connected by fusión 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 the ISO 16486 series, this document is applicable to PA-U fittings, their joints, joints with components of PA-U and joints with mechanical fittings of other materials, and to the following fitting types: fusion fittings (electrofusion fittings and butt fusion fittings), and transition fittings.