| 摘要 |
PROBLEM TO BE SOLVED: To provide a tap having a shape which is formed so as to make cutting resistance small in screw hole boring, and the shape enabling effective elimination of swarf, and yields resistivity against breakage. SOLUTION: A cutting edge part is formed by a chamfer part of a incomplete thread, and a complete thread part of not less than 4 piches and not more than 6 piches. The cutting edge is coated with a hard film such as a diamond film or a diamantine carbon film, and the cutting edge part is divided circumferentially by a plurality of slots. Also, at a rear end side of the cutting edge part, a minor diameter part which is smaller than a minor diameter of the complete thread part is made. The minor diameter part is not less than 45% of a thread ridge diameter of the complete thread part. Furthermore, as an another shape of the rear end side of the cutting edge part, a screw shaped run off which is continuous with the complete thread part is made, and is tapered so as to become the diameter smaller as parting from the cutting edge part.
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