| 摘要 |
A drill comprising a drill shank having a taper portion adjacent to a threaded portion provided on the rear or basal portion of the shank. When the drill is screwed into an axial hole in a drill holder of a drilling machine, the opening edge or inner tapered wall of the axial hole of the drill holder bites into the taper portion of the drill shank, consequently to bring the drill into firm connection with the drill holder of the drilling machine.
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