A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.

A method for producing an entirely stainless steel, high-strength self-drilling screw that does not need heat treatment downstream of manufacturing to improve material hardness. A stainless steel wire section blank is provided. A screw head is cold-formed at a first end. Subsequently, the diameter at the second end section is reduced by cold forming. A drill tip is produced at the second end by a tweaking movement transverse to the longitudinal axis. Subsequently, the drill tip is finished. Any protruding material flags remaining on the drill tip cutting edges are sheared off during subsequent thread rolling. During preforming, contour edges are formed in the region of the subsequent cutting edges, with the remaining material thickness between 0.3 mm and 1.0 mm. The drill tip final forming forms these contour edges into the cutting edges, and the remaining material thickness between the cutting edge and the material flag is between 0.05 mm and 0.2 mm.

A method for producing an entirely stainless steel, high-strength self-drilling screw that does not need heat treatment downstream of manufacturing to improve material hardness. A stainless steel wire section blank is provided. A screw head is cold-formed at a first end. Subsequently, the diameter at the second end section is reduced by cold forming. A drill tip is produced at the second end by a tweaking movement transverse to the longitudinal axis. Subsequently, the drill tip is finished. Any protruding material flags remaining on the drill tip cutting edges are sheared off during subsequent thread rolling. During preforming, contour edges are formed in the region of the subsequent cutting edges, with the remaining material thickness between 0.3 mm and 1.0 mm. The drill tip final forming forms these contour edges into the cutting edges, and the remaining material thickness between the cutting edge and the material flag is between 0.05 mm and 0.2 mm.

A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.

A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.

A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.

A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.

A rolling machine has a rolling die 4 that forms a male screw by pressing a steering shaft 14 which is an object to be rolled and plastically deforming an outer peripheral surface of the steering shaft 14 while rotating in contact with the outer peripheral surface of the steering shaft 14, a main spindle 3 inserted into a penetration hole 10 of the rolling die 4 and transmitting a rotation force to the rolling die 4, a key groove and a key which restrict a relative rotation between the rolling die 4 and the main spindle 3, a spiral oil groove 16 provided on an inner peripheral surface of the penetration hole 10 or an outer peripheral surface of the main spindle and extending from one end portion 10b side in an axial direction of the penetration hole in an inner axial direction of the penetration hole.

A rolling machine has a rolling die 4 that forms a male screw by pressing a steering shaft 14 which is an object to be rolled and plastically deforming an outer peripheral surface of the steering shaft 14 while rotating in contact with the outer peripheral surface of the steering shaft 14, a main spindle 3 inserted into a penetration hole 10 of the rolling die 4 and transmitting a rotation force to the rolling die 4, a key groove and a key which restrict a relative rotation between the rolling die 4 and the main spindle 3, a spiral oil groove 16 provided on an inner peripheral surface of the penetration hole 10 or an outer peripheral surface of the main spindle and extending from one end portion 10b side in an axial direction of the penetration hole in an inner axial direction of the penetration hole.

A method of manufacturing a banjo bolt including a shaft portion including a vertical hole provided in the shaft portion and extending in a first direction, includes forming a first lateral hole and a second lateral hole by processing the shaft portion from a first side in a second direction crossing the first direction, the first lateral hole extending in the second direction and connecting an outside of the shaft portion and the vertical hole, the second lateral hole being located on an opposite side of the first lateral hole with respect to the vertical hole and extending in the second direction and connecting the outside of the shaft portion and the vertical hole, the second lateral hole being larger than the first lateral hole and overlapping the entire first lateral hole when viewed along the second direction, and forming a third lateral hole by processing a portion of the shaft portion where the first lateral hole is formed from a second side in the second direction through the second lateral hole, the third lateral hole being larger than the first lateral hole and similar to the second lateral hole when viewed along the second direction.