The object of this standard is to define the dimensions of a series of standard ball and socket couplings using the standard locking devices (see IEC 60372) in order to permit the assembly of insulators or metal fittings supplied by different manufacturers. This standard applies to string insulator units of the cap and pin and long rod types and their associated metal fittings. For the pin ball and the socket, dimensions apply to the finished product after any surface treatment. Extreme positions of the pin ball in the socket are given in Annex A. Typical examples of gauges for checking the dimensions of pin balls and sockets are given in Annex B. NOTE Only the dimensions necessary for assembly are dealt with in this standard. Properties of material and working loads are not specified. The co-ordination of dimensions with strength classes is specified in IEC 60305 and IEC 60433.