PURPOSE: To dispense with cutting formation from a round bar and decrease working processes and cost, by elongating a circular pipe to a prescribed length and providing conjoining hammered portions at both the ends of the pipe.

CONSTITUTION: A circular pipe 1 is elongated to a prescribed length. At one end of the pipe, a thick hammered portion 2 having a screw 4 inside is provided. At the other end of the pipe, another hammered portion 3 including an open part 8 expanded to a large thickness if provided. One of the tubular hammered portions 2, 3 is screw-engaged with an outer joint 5 and the other is fitted with an inner joint 9 so that the pipe 1 is coupled.