| 摘要 |
A drill screw having primary and secondary cutting edges on opposite sides of its longitudinal axis, with the primary cutting edge offset so that it contacts the work-piece first, at a position displaced laterally from the screw axis, and produces initial very rapid drilling of an opening through the work-piece, followed by a period of drilling by both cutting edges. A conical portion is also preferably provided on the screw which extends divergingly from the cutting edges toward the head end of the screw until its diameter matches the root diameter of the screw.
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