PREFACE to the third edition ?C 1969This International Standard contains the recommendations of the IEC in regard to lamp caps and holders in general use today@ together with relevant gauges@ with the object of securing international interchangeability. The gauges illustrated@ although generally accepted in principle@ are not necessarily the only form in which they can be made.In view of the increased number of Standard Sheets contained in IEC 60061@ the opportunity has been taken@ at the issue of this third edition@ to split the single publication into three parts@ numbered IEC 60061-1@ IEC 60061-2@ IEC 60061-3@ covering lamp caps@ Iampholders and gauges respectively. A supplementary part ??Guidelines and general information??@ numbered IEC 60061-4@ was added in 1990.In order to facilitate use@ each part contains a dated Contents list of the sheets included in that part. An updated Contents list will be included in every additional annex.IEC work on Lamp caps and holders@ and gauges@ dates back to 1925@ when an Advisory Committee (No. 6) for the standardization of lamp caps and holders was appointed with the object of securing international interchangeability. In this work Advisory Committee No. 6 profited by the active co-operation of the Independent Committee on Standardization of Lamp Caps and Holders (INDECO) up to May 1939. During the war years@ 1939-1945@ no meetings could be held and it was not until early in 1947 that it was found possible to resume activities.At this time the IEC Central Office wrote to the National Committees proposing the appointment of a small preparatory committee of representatives of manufacturers of both lamp caps and lampholders. The outcome of this proposal was that a Committee was duly formed comprising experts from the majority of countries formerly represented by INDECO@ with the addition of an expert from the U.S.A.@ and@ at a later date@ a representative from Sweden. This Experts Preparatory Committee (EPC) took into account the work of the INDECO and the resultant recommendations were submitted to the National Committees by the full subcommittee on Lamp caps and holders (34B) for approval.