Shown here is the 75 material at 0 A. A core with no gap has a permeability of about 475 at 8 MHz, and just over 300 with a gap two-thousandths of an inch at 8 MHz. At 5 A and no gap, permeability is at less than 30, but still has 300 at 8 MHz with a two-thousandths of an inch gap.