Abstract: A novel threaded fastener is provided having an elongated shank portion with a first end and a second end opposed to the first end, and a helical thread in the form of a continuous helical ridge that is arranged on an external surface of the shank portion. The helical thread includes an asymmetrical threaded portion that has a progressively increasing axial displacement of a pressure flank of the helical thread between the first end and the second end of the shank portion, and a progressively decreasing axial displacement of a non-pressure flank of the helical thread between the first end and the second end of the shank portion. When assembled, the novel threaded fastener has a clamping force distribution that is evenly distributed on the helical threads along its axis in the direction of force transmission reducing the risk of self-loosening and increasing fatigue resistance.

Abstract: Disclosed is a screw head having a slot (2) in the upper surface of the screw head, an upper peripheral wall (9) of hexalobular planform extending down into the screw head, the upper peripheral wall (9) being parallel or near parallel to the axis of the screw, a sloping transition surface (15) extending downwardly and inwardly with respect to the lower edge of the upper peripheral wall (9), and a tapered recess (11) extending downwardly from the lower edge of the sloping transition surface (15), in which the dimensions of the screw head are such that when the screw head is engaged by a tool (6) having upper (16) and lower engagement (17) sections, there is a ‘stick fit’ between the surface of the tapered recess (11) and the external surface of the lower engagement section (17), and there is no engagement with the sloping transition surface (15).

Abstract: Disclosed is a screw head having a slot (2) in the upper surface of the screw head, an upper peripheral wall (9) of hexalobular planform extending down into the screw head, the upper peripheral wall (9) being parallel or near parallel to the axis of the screw, a sloping transition surface (15) extending downwardly and inwardly with respect to the lower edge of the upper peripheral wall (9), and a tapered recess (11) extending downwardly from the lower edge of the sloping transition surface (15), in which the dimensions of the screw head are such that when the screw head is engaged by a tool (6) having upper (16) and lower engagement (17) sections, there is a ‘stick fit’ between the surface of the tapered recess (11) and the external surface of the lower engagement section (17), and there is no engagement with the sloping transition surface (15).