PURPOSE: To prevent rotation deviation and rolling by a notched groove and to roll satifactory round screw threads with the notched groove to a stock by rolling the stock having the notched groove in a thread forming part by integral dies having serration forming parts adjacently to the thread forming part.
CONSTITUTION: The stock 1 having a notched part 4 such as key groove is press-rolled by one set of the thread rolling dies 5 for rolling having the serra tion parts 7 adjacent to the thread forming parts to form a screw thread array 2. The serrations 8 are transferred to a root part 3 of the notchless circular stock, by which the rotation deviation by the notched part 4 is eliminated and the generation of the rolling is prevented; in addition, the screw thread array 2 is formed to the satisfactorily round shape. Since the key groove 4 is not cut after the formation of the thread array 2, the need for finishing is eliminated and the efficiency of the operation is improved.
O S G KK