| 摘要 |
PROBLEM TO BE SOLVED: To obtain a driving hole shape of a cross recessed head screw which bites well the driving hole and accurately gets a preliminarily preset screwing torque. SOLUTION: The driving hole is constituted of an engaging groove 11 in which an engaging blade 21 is fitted and an incoming hole 15 in which a driver bit 20 enters. The engaging face 13 of the engaging groove 11 is formed parallel to its center line or so that the central side becomes wide. The engaging faces 13 are connected together on the arcuate guide face 14 protruding the engaging face 13 to the incoming hole 15. Further, the engaging blade 21 is fitted in between the guide faces 13 of the both sides of the engaging groove 11, and the base of the engaging blade 21 is loosely fitted to the guide face 14. Owing to the driving hole shape of the cross recessed head screw, a driver bit is used without changing into a special shape and even when the screw is fastened by using an ordinary driver bit, no comeout phenomenon is brought at the completion of fastening work and further variation of screw fastening torque is eliminated and hence, frequency of defective products decreases. COPYRIGHT: (C)2003,JPO
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