To realize the manufacturing of an insert fitment, which can withstand against both detent and locking load only by forging.

A parallel deeply vertically grooved knurl 2 is formed at the intermediate part on the peripheral surface of a cylindrical body 1, in which a center hole 1a for installing onto other member. At the lower edge of the parallel knurl 2, an annular groove 3 is formed. Further, after the tip part of a metal stock 10 having certain dimensions is pre-formed somewhat convergent 11, the outer peripheral surface of the metal stock 10 is formed into a large diameter part 12 and a small diameter part 13. In addition, on the upper and lower surfaces of the resultant metal stock, recessed parts 14 are formed. Further, a parallel vertically grooved knurl 2 is formed at the lower half part of the large diameter part 12 of the metal stock 10. Furthermore, the recessed parts 14 are pierced. The small diameter part 13 of the parallel-knurled and pierced metal stock 10 is squeezingly formed so as to be expanded into an expanded diameter part 14, the diameter of which is equal to that of the large diameter part 12. Finally, the annular groove 3 is formed at the lower end of the parallel knurl 2.