This standard applies to string insulator units of the cap and pin type and also of the long rod type as well as the fittings used with such insulators. The object of this standard is to define the dimensions of a series of clevis and tongue couplings to permit the assembly of insulators or fittings supplied by different manufacturers. NOTE 1 IEC 60305 gives the co-ordination between the standardized dimensions of Table 1 and the strength classes of cap and pin insulator. IEC 60433 gives the co-ordination between the standardized dimensions of Table 2 and the strength classes of long rod insulators. NOTE 2 If the dimensions given in Table 1 are not sufficient, it is recommended to use coupling pins of 25 mm, 28 mm and 32 mm which probably will be used for higher strength classes(see IEC 60305).