This standard specifies the physical and magnetic dimensions of E-cores made of magnetic oxides for use in high flux density applications. This range specifically covers cores designed for use in power transformers, for example for switched mode power supplies operating typically at 25 kHz switching frequency; it lists preferred dimensions of these cores together with their tolerances as far as these are of importance for mechanical and electrical interchangeability.
GSO IEC 60647:2014 history
2014GSO IEC 60647:2014 Dimensions for magnetic oxide cores intended for use in power supplies (EC-cores)