To provide an inexpensive product which can be assembled easily and accurately by omitting manufacturing processes, and thus reducing the number of part items.

This manufacturing method includes a first process in which, after a base is cut into a predetermined length, a rod-shaped member 16 is formed by shaving the surface of the base over a predetermined length while a projecting part 15 is formed to continue to the outer periphery of one end of the rod-shaped member; a second process in which an annular member 17 for fitting over the rod-shaped member formed by the first process is formed by shaving or blanking the base; and a third process in which the annular member 17 formed by the second process is fitted around the rod-shaped member and one side 17 a of the annular member is made to abut to the projecting part provided at one end of the rod-shaped member, and thereafter the other side 17b of the annular member near its inner periphery is caulked by an appropriate means and pressed 18 against the outer peripheral surface of the rod- shaped member.