| 摘要 |
A drill insert has a polygon plate-shaped body that defines a top face and a central shaft extending substantially perpendicular to the top face. A pair of first cutting edges are formed on the top face in a dot symmetrical relation with respect to the central shaft. A pair of second cutting edges are formed on the top face in a dot symmetrical relation with respect to the central shaft. The second cutting edges are disposed adjacent to the first cutting edges. A projected cutting edge portion is provided in each of the second cutting edges. The projected cutting edge portion outwardly projects from each of the second cutting edges in a radial direction with respect to the central shaft.
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