Cap Nomenclature

Because of the large variety of different cap types a comprehensive system of nomenclature has been developed by the International Electrotechnical Commission. It commences with a single letter to denote the general type of cap, which may be followed by additional letters to denote a sub-category. The second part is a number which denotes the shell diameter (or pin spacing) in millimetres. The third part of the code is a small letter to indicate the number of contact plates (or pins). Special modifications to the basic design may be indicated by a character following a hyphen. These three or four parts are generally sufficient to define the cap as far as the end user is concerned, for compatibility purposes. However to provide a full definition certain other dimensions may be necessary, and these follow a forward slash (such as, for example, the length of the cap). The list of all general lighting cap types is maintained in the international standard IEC 60061.