This part of IEC 62317 specifies the dimensions that are of importance for mechanical interchangeability for a preferred range of ring-cores@ also called toroid cores@ and the effective parameter values to be used in calculations involving them. The selection of core sizes for this document is based on the philosophy of including those sizes which are industrial standards@ meaning that they are in broad-based use within industry. See IEC 62317-1 for more detail concerning the philosophy of selecting core sizes to be included.