To facilitate a fastening operation by setting an angle to be relatively small between adjacent blades of a tapered cross locking bit which is inserted into a cross groove of a screw, and pressing and engaging this cross locking bit with the cross groove for crimping.

In cutting and forming a groove portion 2a, an angle is set to be relatively small between adjacent blades of a tapered cross locking bit 2 which is inserted into a cross groove 1a of a screw 1. In other word, a pair of groove portion 2a positioned facing each other so that the angle is set about 90° between the adjacent blades of the tapered cross locking bit 2 which is inserted into a cross groove 1a of a screw 1. Thus, the tapered cross locking bit 2 is inserted into the cross groove 1a of a screw 1, and is pressed and engaged with the cross groove 1a via the tapered cross locking bit 2 with a wedge operation for crimping. Thus, regardless of property of machine screws, all machine screws can be certainly held.