Magnetec Cool Blue nanocrystalline cores from MH&W International are intended for use as common mode chokes. The cores provide a range of permeability of 25,000-90,000 at 10 KHz, and a saturation flux density of 1,200 mT. The smallest core for high power motor applications has an outside diameter of 63 mm and inside diameter of 50 mm. The largest core has a 500 mm OD and 450 mm ID. The standard thickness of all Cool Blue cores is 30 mm. From $40.