Abstract: Provided are a screw (11) which can significantly reduce the cam-out if a dedicated driver bit is (14) used, and which also allows the use of a driver (6) bit for a standard cross recess and can reduce the cam-out to some extent, and a dedicated driver bit (14) for such a screw (11). Of a recess (13), a central portion (17) and proximal end side portions (18a) of blade engaging portions (18) are configured in the same manner as in a standard cross recess. The tightening side sidewall (20) or the loosening side sidewall (21) in the distal end side portions (18b) of blade engaging portions (18) are bent at an oblique angle. A dedicated driver bit has a corresponding cross-sectional configuration to that of the recess (13). Because the dedicated driver bit is hard to tilt relative to the screw (11) and the engagement between the blades (19) of the driver bit (14) and the blade engaging portions (18) is improved, the cam-out becomes hard to occur.

Abstract: Provided are a screw (11) which can significantly reduce the cam-out if a dedicated driver bit is (14) used, and which also allows the use of a driver (6) bit for a standard cross recess and can reduce the cam-out to some extent, and a dedicated driver bit (14) for such a screw (11). Of a recess (13), a central portion (17) and proximal end side portions (18a) of blade engaging portions (18) are configured in the same manner as in a standard cross recess. The tightening side sidewall (20) or the loosening side sidewall (21) in the distal end side portions (18b) of blade engaging portions (18) are bent at an oblique angle. A dedicated driver bit has a corresponding cross-sectional configuration to that of the recess (13). Because the dedicated driver bit is hard to tilt relative to the screw (11) and the engagement between the blades (19) of the driver bit (14) and the blade engaging portions (18) is improved, the cam-out becomes hard to occur.

Abstract: A male screw which has a protrusion protruding from a thread thereof at least with regard to the normal direction to a flank of the thread. To obtain such male screw, a blank is introduced between rolling dies which are moved relative to one another and is rolled between the rolling dies to be formed with a thread. In this thread rolling process, the rolling pressure on an area of a die face of at least one of the rolling dies is determined to be higher than that in an ordinary thread rolling process and the rear end portion of the area of the die face is made to bite into the blank, causing the corresponding portion of the blank to be forced out to form the protrusion.

Abstract: A male screw which has a protrusion protruding from a thread thereof at least with regard to the normal direction to a flank of the thread. To obtain such male screw, a blank is introduced between rolling dies which are moved relative to one another and is rolled between the rolling dies to be formed with a thread. In this thread rolling process, the rolling pressure on an area of a die face of at least one of the rolling dies is determined to be higher than that in ordinary thread rolling process and the rear end portion of the area of the die face is made to bite into the blank, causing the corresponding portion of the blank to be forced out to form the protrusion.