Patent ID: 6886433
Filing Date: 2005-05-03
Classification: B21K,B25B,F16B

Abstract:
1. 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 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; 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.