This part of ISO 11363 specifies dimensions and tolerances for taper screw threads of nominal diameter 17,4 mm (designated 17E) and 25,8 mm (designated 25E) used for the connection of valves to gas cylinders. It does not cover the connection requirements for: - mechanical strength; - gas tightness; - capability of repeated assembly and dismounting operations. Gauge inspection is covered by ISO 11363-2.