Power Inductive EFD Cores Fair-Rite Power Inductive EFD (Economical Flat Design) Cores have been designed to maximize volume in a low profile geometry. This allows maximum throughput power density with reasonably low mass for board-level installation. Fair-Rite Products EFD Cores can be supplied with the center post gapped to mechanical specifications as well as an AL value. EFD Cores are available in a range of sizes from EFD10 to EFD30 and 3 materials with Initial Permeability ranging from 2300 to 3000.