This part of IEC 62317 specifies the dimensions that are of importance for mechanical interchangeability for a preferred range of EFD-cores, the essential dimensions of coil formers to be used with them, and the effective parameter values to be used in calculations involving them. The selection of core sizes for this standard is based on the philosophy of including those sizes which are industrial standards, either by inclusion in national standards, or by broad-based use in industry. See IEC 62317-1 for more detail concerning the philosophy of selecting core sizes to be included. The general considerations that the design of this range of cores is based upon are given in Annex A.