| 摘要 |
A drill including a cylindrical main body and a shank. The cylindrical main body has: (a) flutes providing cutting edges at an axially distal end of the cylindrical main body; (b) lands each provided by a peripheral portion of the cylindrical main body and located between the flutes; and (c) a web provided by a central portion of the cylindrical main body which joins the lands and extends in an axial direction of the cylindrical main body. The web includes a back-tapered portion which is provided by at least an axially distal end portion of the web, such that a thickness of the web in the back-tapered portion is gradually or continuously reduced as viewed in a direction away from the axially distal end of the cylindrical main body toward the shank.
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