To provide new screw dropout preventive technology which can prevent the unexpected dropout of a screw mounted at the tip of a screwdriver and execute screwing/unscrewing operation without trouble if the space through which the outside diameter dimension of a screw head part passes is secured.
In a screw body 11, a head part 3 having a cross slot 31 coaxially keeping an intersection is formed on the other end surface of a shaft part 2 with a male screw 22 engraved in an outer peripheral wall surface extending over a specified area from a tip side 21. A drop-off preventive screw in which a columnar or cylindrical fitting hole 4 with a specified depth is punched so as to be concentrically arranged at the axial center of the shaft part 2 and a blade having a blade edge 61 engageable with the cross slot 31 in the head part 3 of the dropout preventive screw are provided to the bottom center of the cross slot 31 in the head part 3. A dropout preventive screwdriver which is concentrically arranged at the axial center of the blade 6 and which keeps a columnar or cylindrical fitting protrusion 7 fitable in the fitting hole 4 in the head part 3 of the screw is provided to the center of the blade edge 61 tip of the blade 6.
COPYRIGHT: (C)2007,JPO&INPIT
