To shorten the length of respective parts, make the stroke of a compression device required in manufacturing parts small, and facilitate its execution by manufacturing the entirety of an insert in a manner being divided into a plurality of parts in the longitudinal direction.

A binder is blended in material powder to then be put in a mold in the form of granules, and they are compressed by the use of a compression device in the longitudinal direction for forming a tip cylindrical part 13. In a similar way, a recessed cylindrical part is formed, the inner surface of which is formed with a female screw 15 through cutting work in use of a tapping machine so as to form a recessed cylindrical part 14. Next, the tip cylindrical part 13 is superimposed on the recessed cylindrical part 14 to subsequently be put in an electric automatic continuous furnace, then increasing the temperature gradually for sintering and joining both of them. After that, they are annealed and removed therefrom in order to complete an insert 10.