| 摘要 |
PROBLEM TO BE SOLVED: To provide a tap capable of accurately machining an internal thread in a thin nut blank. SOLUTION: In this tap 1 advancing, while rotating, to machine the internal thread in a prepared hole H of the nut blank N, lands A to F are provided at intervals in the rotating direction. Of each land A to F, every other land A, C and E along the rotating direction is provided with a rough screw thread machining part 2 constituted of a plurality of threads A1 to A15 having constant effective diameters d1. Each of the remaining lands B, D and F is provided with a finishing part 3 constituted of a plurality of threads B8 to B18 having larger effective diameters d2 than those of the threads A1 to A15 of the rough screw thread machining part 2 and the constant effective diameters d2. In the finishing part 3, a position on a rear side of the thread A1 at a front end of the rough screw thread machining part 2 by 5 threads or more is made as the thread B8 at the front end. COPYRIGHT: (C)2010,JPO&INPIT
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