To provide a screw, and a screwdriver for tightening a screw, in which a bit of a screwdriver can be easily inserted to achieve excellent workability, in which large torque can be transmitted from the screwdriver when the screw is tightened, in which the screwdriver is prevented from unexpectedly floating to damage recessed parts, in which the screw can be tightened and loosened, and in which strength is structurally high to shearing.
A plurality of the recessed parts 3 are provided in an upper surface of a screw head part 2 of a screw part 1 around an axial center Z for the bit 8 of the screwdriver B to be inserted, and between the recessed parts, engagement wall parts 4 in which the bit is engaged are provided in this screw. The recessed part has a tapered cross section as a whole, and a perpendicular engagement surface 5 parallel to a bisector M in a cross direction of the engagement wall part drawn through the axial center in one inner side surface of the screw on the tightening direction side P close to the outer circumference is formed in a thickness direction T of the screw head part. For the screwdriver B, the bit 8 is provided to the axial center Z' roughly in a similar form to the recessed part 4 provided in the screw head part 2, and on the outer circumferential side of the bit 8, a drive perpendicular engagement surface 9 is provided to be surface-engaged with the perpendicular engagement surface 5.
Hiroshi Ochi
Sadao Matsumura
Isamu Kakiuchi