PURPOSE: To prevent twisting in the formation of the spiral nodes on the surface of steel bars by inclining roll calibers in such a way that the twisting forces in opposite directions are acted upon the steel bars by the moment of the difference in peripheral speeds generated between upper roll calibers and lower roll calibers thereby rolling the steel bars.

CONSTITUTION: Calibers 3, 4 having prescribed lead angles at prescribed pitches are engraved respectively to the caliber 1-1 of an upper roll 1 and the caliber 2-1 of a lower roll 2. In the case of producing screw reinforcing bars of right- hand screws with said rolls 1, 2, the bars are rolled with the calibers 1-1, 2-1 of the upper and lower rolls which are inclined by an angle θ of inclination to the side of the screw direction with respect to the diametral centerline O of the rolls. Then the twisting force in the direction opposite from the twisting force occuring in the inclination of the calibers 3, 4 is generated by the moment of a difference in peripheral speeds generated between the calibers 1-1, 2-1. The rolling free from twisting is accomplished by balancing of the moment of a difference in peripheral speeds and the twisting force occuring in the inclination of the calibers.