This International Standard specifies the characteristics of the 90 [89 mm (3,5") diameter] semi-trailer fifth wheel kingpin used for coupling extra-heavy-duty vehicles exceeding the limitations of weight generally laid down by official requirements. It is applicable to fifth wheel kingpins intended for engaging 90 fifth wheels as defined in ISO 3842[1]. This International Standard also specifies the dimensional characteristics required for mounting and interchangeability. NOTE The dimensions of the 50 semi-trailer fifth wheel kingpin, normally used to couple semi-trailers to tractors in compliance with mass limitations usually set by compulsory regulations, are given in ISO 337[2].