Abstract: Steel workpieces, such as thread-forming screws and bolts, tapping tools, and the like, are hardened in localized areas to controlled depths of hardening by utilizing loose electromagnetic coupling between the workpiece and the induction coil. The loose coupling reduces the criticality of the positional relationship between the workpiece and coil and also allows unidirectional axial through-feed of headed workpieces. A high degree of symmetry of hardening around each piece and uniformity of hardening from piece to piece at high production speeds is accomplished.