Prescribes specified values for the mechanical characteristics of the composite string insulator units. Defines the main dimensions of the couplings to be used on the composite string insulator units in order to permit the assembly of insulators of fittings supplied by different manufacturers and to allow, whenever practical, interchangeability with existing installations. It also defines a standard designation system for composite string insulator units. The contents of the corrigendum of November 2007 have been included in this copy.