PURPOSE: To compactly combine a collar to a pin in the minimum length with satisfactory strength and adaptability by bringing a rotating die which has the row of inclined ribs forming threads into pressure-contact with a threaded end and rolling it to form threads.

CONSTITUTION: A stock 10 is preliminarily formed so as to have a head 11, a central line 12 and a cylindrical shank 13. Also, a groove 15 is formed by cutting so as to form a shoulder with reducing diameter. A radius 17 is put on the smallest diameter position of the shoulder 16. The other shoulder 18 is formed by cutting in the other side of the groove 15. An end part 19 is cut or formed in order to make rotating threads. The region including the radius 17 is rolled for work-hardening with a rotating device. Threads 25 are successively formed in the end part 19 after the hardening operation. Thereupon, since the groove 15 exists, incomplete threads are not formed exceeding the length of the minimum limit i.e., 180°. Thus, the collar 30 and the pin 45 are combined vary compactly in the minimum length with satisfactory strength and adaptability.