| 摘要 |
PROBLEM TO BE SOLVED: To provide a core drill having excellent sharpness from an early stage, and stably boring. SOLUTION: An abrasive grain layer 5, namely a segment 9 is adhered on an upper end surface 5 of a shank 3. In the segment, a groove 15 extending in a circumferential direction of a circle concentric with the shank is formed on the upper end surface.
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