EPCOS B65981 PQ50/50 Ferrite Cores EPCOS B65981 PQ50/50 Ferrite cores have optimised round leg and wider outer surface to conventional cores. The round leg on these ferrite cores reduces winding length and the wider surface area lowers the thermal resistance by offering a larger area for heat dissipation. The shape also produces better shielding to the winding. To IEC 62317-13.