| 摘要 |
PROBLEM TO BE SOLVED: To provide a screwdriver bit having a shape matched with the coupling groove of a screw and reliably transmitting driving force. SOLUTION: A blade part 10 having a cross-shaped cross section couplable with the coupling hole 20 of the screw 2 is formed, side walls 14 are connected by a circular arc-shaped connecting groove 13 at the base part of the blade part 10, the radius R of the connecting groove 13 is made such a size that the circular arc is located on the center side than the distance b of the narrowest part pinching at least the center of the screw 2, and both ends of the circular arc are connected to both side walls 14 in this screwdriver bit for a screw with a cross hole. The blade part can firmly bite into the coupling groove between the coupling hole of the screw and the screwdriver bit. The area receiving the driving force of the screwdriver bit is not decreased, the driving force is not concentrated at one point, and the screw and the screwdriver bit are hardly broken.
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