To improve the accuracy of a female thread and the grindability of a tap by forming the female thread and leveling a seam part in one process.
The valley of a bevel lead part 13 in a thread section is made shallower than that of a parallel thread section 14 so as to become equal to the inner diameter of the female thread, and a radial section 17 is formed to push up the top section of the female thread when the reamer body is reversed to make it possible to form the female thread and level a seam part in one process even when making a blind hole and the formation of the female thread and the machining of the inner diameter section of the female thread are performed in the same process, providing concentricity in the female thread and tap body.
YOKOYAMA ISAO
SATO KAZUTOSHI
