| 摘要 |
A cold forming tap with an internal finish cutting edge including an external thread portion having radially outwardly protruding portions and relief portions which are alternately located in a helical direction in which an external thread extends, the protruding portions capable of being forced into a surface of a prepared hole which has been previously formed through a workpiece, to thereby form an internal thread on the surface, and wherein an improvement comprises: at least one of the protruding portions having a root diameter larger than that of the other of the protruding portions, the at least one of the protruding portions being removed down to a root of the external thread, and a flute being formed in a portion corresponding to the root of the at least one of the protruding portions, so as to provide the cutting edge in the portion corresponding to the root. |
