COIL1010-0.22 is a ferrite toroid core, manufactured by an American manufacturer called Ferrocore. It is a low cost, low profile, high permeability ferrite core, optimized for use in medium frequency, high frequency inductors. It has a high resistance to saturation, allowing for very efficient operation at frequencies of up to 1MHz. The material is RoHS compliant, making it safe to use in most applications. Ferrocore state that it is ideal for use in transformers, filters, chokes, and other inductive components.