THREAD-FORMING TAP

Since a sharp crest 40 having a triangular cross-sectional shape is provided in a top portion of a thread ridge 10 of an external thread in the leading portion 24, the thread ridge 18 is easily caused to bite into an inner-wall-surface layer portion of a prepared hole of a workpiece in a tapping operation, thereby reducing torque and thrust load during the tapping operation. Further, since a pair of side surfaces 42, 44 of the sharp crest 40 are inclined by respective inclination angles β1, β2 that are larger than flank angles α1, α2 of the thread ridge 18, an angle (internal angle) of a top end portion 46 in which the side surfaces 42, 44 intersect with each other is larger than an angle defined between extensions of the flanks 30, 32, thereby restraining breakage or the like due to lack of strength of the top portion. That is, it is possible to restrain reduction of the tool life due to wear or the like, by reducing the torque and the thrust load during the tapping operation while assuring the strength of the top portion of the thread ridge 18.