The screwdriver (10) has an enlarged head (11) with six flat faces and this regular hexagonal head is devoid of taper. The head may be gripped by the chuck of a boring machine. The chuck head is connected via a cylindrical portion to a conical portion which tapers down to a smaller diameter. The smaller diameter portion blends into a hexagonal portion (12) which has a very slight taper, especially a taper angle of 3.6 degrees. The hexagonal portion is designed to fit into the blind bore in the head of the screw.
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