| 摘要 |
A thread forming tap which is capable of reducing tapping torque as well as improving durability by avoiding an increase of an apparent area of margins of external thread that causes interference with a grinding stone. The thread forming tap has an external thread in a screw shape with alternately linked margins and reliefs for forming an internal thread by plastic deformation upon having the margins of the external thread bite into a surface of a prepared hole of a workpiece. A helix of the margins of the external thread is in a direction opposite to a direction of a helix of the external thread relative to an axis of the tap.
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