| 摘要 |
PURPOSE: To guarantee exact guidance of a screw driving tool tip and transmis sion of a large torque, by forming a recess with walls having conical surfaces at the side wall radially displaced from the cylinder surface toward inside or outside at the end of a screw to accept the screw driving tool tip. CONSTITUTION: A recess 2 is formed at the end 1 of a screw to accept a screw driving tool, the side wall 3 of the recess 2 is formed by six arcs 4, the outline of which outwardly turns, and the arcs 4 are mutually connected with inwardly turning arcs 5. Further, a part of the inwardly turning arcs 5 of the side wall 3 is formed into conical surfaces 6. The screw driving tool is provided with a protrusion with a side wall 16, which is formed by outwardly turning arcs 17 and inwardly turning arcs 18 with twice the radius of the arcs 17 arranged between the arcs 17. The radially inside walls are formed into conical surfaces 19, and the free edge 20 of the protrusion 15 is formed into a conical surface.
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