Abstract: An induction coil for the treating of metal parts where the coil carries large currents and is subjected to large forces. The coil has two layers of metal, the layer nearest the metal part being made of high conductivity and the other layer being made of a metal having an electrical conductivity less than that of copper and having a Young's Modulus at least 20% greater than the Young's Modulus of the metal of the layer nearest the metal part. The layer of metal nearest the metal part has a thickness at least equal to the reference depth of the current in such metal and preferably, has a thickness from 1.5 to 10 times such reference depth. Preferably, also, the surfaces of the other layer, except possibly those relatively remote from the principal currents, are covered by the high conductivity metal having a thickness at least equal to such reference depth.