Abstract: A process for forming a screw thread on a corrugated bar used in concrete reinforcement joints such as anchor bolt joints. The ribs and flank fillets are removed from the end portion of the corrugated bar to be threaded. The end portion is then heated in a controlled manner such that the temperature of the end portion is highest at the end and falls smoothly toward the beginning of the ribless portion of the bar. The bar is immovably locked in place and the end portion is pressed by a movable cylindrical mold. Due to the temperature difference along the end portion, hot upsetting sets in at the end and advances toward the beginning of the ribless portion and the cross-sectional area of the end portion expands to become equal to an inner diameter of the mold. A screw thread is then formed on the end portion of the bar, the cross-sectional area of the screw thread being at least equal to the cross-sectional area of a remainder of the bar and the thread being longer than a diameter of the bar.