Abstract: A method of forming precision openings in hardened steel workpieces is disclosed. The method generally includes drilling nominal size openings in the workpiece while it is in a soft condition. Thereafter, sizing plugs formed from a material having a strength greater than that of the steel body during a predetermined range of temperatures are press-fitted in the openings. With the plugs in position, the body is heat treated to harden it. Subsequently, the plugs are removed and the resulting openings are found to be of an extremely uniform size without the wide variations present when hardening is performed without the sizing plugs.