Abstract: A threading device which can cut a uniform and symmetrical screw thread in the outer surface of a round bar or tube includes a die nut having internal cutting threads and two axial holes and a guide ring which includes two axial roll pins extending away from a rear face thereof and which are capable of extending into the axial holes in the die nut without play to align the axis of the guide ring with the axis of the die nut. The guide ring will act to maintain the axis of the die nut coaxial with the axis of a round bar or tube which extends through the bore of the guide ring and contacts the cutting threads in the die nut. The die nut (together with the guide ring) can be manually rotated to cut a screw thread in a round bar or tube by means of a conventional wrench.