Abstract: An induction heater has a conductor loop (1) in which a large alternating current is induced by a toroidal primary transformer (8). An annular secondary magnetic core (4) encircles a straight length of the conductor loop (1) and is itself enclosed by inner and outer cylinders (2 and 5) interconnected by annular end plates (6 and 9). The current in the conductor (1) produces magnetic flux in the core (4) which in turn produces axial heating currents in the cylinders (2 and 5). The inner cylinder (5) may have heated fins (3). An alternative embodiment has an inductively heated screw.