Combination of screw and screw driver bit and header punch for its manufacture

A plus-minus screw, comprising:

• a screw shaft;
• a screw head part defining a head surface that extends in substantially an orthogonal direction with respect to a longitudinal axis of the screw shaft;
• a cross-shaped bit-fitting groove including respective groove portions that intersect in a center section of the head surface;
• said bit-fitting groove including an end wall part that extends from the head surface of the screw head part to a prescribed depth in the screw head part, said end wall part having a draft taper γ of about 15° to about 5° with respect to a vertical plane parallel to said longitudinal axis of the screw shaft;
• said bit-fitting groove further including an inclined groove part directed from a lower edge part of said end wall part toward a center of the bit-fitting groove, said inclined groove part being formed with an angle of inclination β of approximately 45° with respect to a horizontal plane orthogonal to said longitudinal axis of the screw shaft;
• said bit-fitting groove further including a conical bottom surface formed with a gentle inclination angle α of approximately 28° with respect to said horizontal plane and extending from said inclined groove part to a bottom of the bit-fitting groove at the center thereof;
• said groove portions having a width defined by opposed side wall parts expanding in a radial direction outward from the center section of the screw head part such that an angle of opening δ between the opposed side wall parts of each of adjacent ones of said groove portions which is slightly sharper than a right angle;
• and
• at least one of the groove portions that intersect in the center section of said head surface is configured as a horizontal groove into which a bit blade of a minus screw driver insertingly engages.

A combination of a screw and a driver bit, comprising:

• the screw, including:
• a screw shaft;
• a screw head part defining a head surface that extends in substantially an orthogonal direction with respect to a longitudinal axis of the screw shaft;
• a cross-shaped bit-fitting groove including respective groove portions that intersect in a center section of the head surface;
• said bit-fitting groove including an end wall part that extends from the head surface of the screw head part to a prescribed depth in the screw head part, said end wall part having a draft taper γ of about 1.5° to about 5° with respect to a vertical plane parallel to said longitudinal axis of the screw shaft;
• said bit-fitting groove further including an inclined groove part directed from a lower edge part of said end wall part toward a center of the bit-fitting groove, said inclined groove part being formed with an angle of inclination β of approximately 45° with respect to a horizontal plane orthogonal to said longitudinal axis of the screw shaft;
• and
• said bit-fitting groove further including a conical bottom surface formed with a gentle inclination angle α of approximately 28° with respect to said horizontal plane and extending from said inclined groove part to a bottom of the bit-fitting groove at the center thereof;
• and
• said groove portions having a width defined by opposed side wall parts expanding in a radial direction outward from the center section of the screw head part such that an angle of opening δ between the opposed side wall parts of each of adjacent ones of said groove portions which is slightly sharper than a right angle;
• and
• the driver bit, including:
• a flat driver blade part configured so as to be engageable with the bit-fitting groove of the screw head part along the end wall part of thereof and having a substantially vertical driver side wall part having a driver tip part formed to expand outwardly;
• and
• a flat driver blade part tip formed as a conical projection having at least one side surface inclining at an angle of inclination θ of between about 25° and about 35° with respect to the horizontal plane.

A combination of plus-minus screw, a flat blade and a driver bit, the combination comprising

• the screw, including:
• a screw shaft;
• a screw head part defining a head surface that extends in substantially an orthogonal direction with respect to a longitudinal axis of the screw shaft;
• a cross-shaped bit-fitting groove including respective groove portions that intersect in a center section of the head surface;
• said bit-fitting groove including an end wall part that extends from the head surface of the screw head part to a prescribed depth in the screw head part, said end wall part having a draft taper γ of about 1.5° to about 5° with respect to a vertical plane parallel to said longitudinal axis of the screw shaft;
• said bit-fitting groove further including an inclined groove part directed from a lower edge part of said end wall part toward a center of the bit-fitting groove, said inclined groove part being formed with an angle of inclination β of approximately 45° with respect to a horizontal plane orthogonal to said longitudinal axis of the screw shaft;
• and
• said bit-fitting groove further including a conical bottom surface formed with a gentle inclination angle α of approximately 28° with respect to said horizontal plane and extending from said inclined groove part to a bottom of the bit-fitting groove at the center thereof;
• said groove portions having a width defined by opposed side wall parts expanding in a radial direction outward from the center section of the screw head part such that an angle of opening δ between the opposed side wall parts of each of adjacent ones of said groove portions which is slightly sharper than a right angle;
• and
• at least one of the groove portions that intersect in the center section of said head surface is configured as a horizontal groove into which a bit blade of a minus screw driver insertingly engages
• the flat blade, including:
• a flat blade part being configured so as to be engageable with the bit-fitting groove of the screw head part along the end wall part thereof and having a substantially vertical side wall part having a tip part formed so as to expand outwardly;
• and
• the driver bit, including:
• a flat driver blade part configured so as to be engageable with the bit-fitting groove of the screw head part along the end wall part of thereof and having a substantially vertical driver side wall part having a driver tip part formed to expand outwardly;
• and
• a flat driver blade part tip formed as a conical projection having at least one side surface inclining at an angle of inclination θ of between about 25° and about 35° with respect to the horizontal plane.

A screw, comprising:

• a screw shaft;
• a screw head part defining a head surface that extends in substantially an orthogonal direction with respect to a longitudinal axis of the screw shaft;
• a cross-shaped bit-fitting groove including respective groove portions that intersect centrally of the head surface;
• said bit-fitting groove including an end wall part that extends from the head surface of the screw head part to a prescribed depth in the screw head part, said end wall part having a draft taper γ of about 1.5° to about 5° with respect to a vertical plane parallel to said longitudinal axis of the screw shaft;
• said bit-fitting groove further including an inclined groove part directed from a lower edge part of said end wall part toward a center of the bit-fitting groove, said inclined groove part being formed with an angle of inclination β of approximately 45° with respect to a horizontal plane orthogonal to said longitudinal axis of the screw shaft;
• and
• said bit-fitting groove further including a conical bottom surface formed with a gentle inclination angle α which is less than said angle of inclination β with respect to said horizontal plane, said conical bottom surface extending from said inclined groove part to a bottom of the bit-fitting groove at the center thereof.