Abstract: A shape of the head part of the screw is improved and performance of insertion of the screw when punched and performance of fastening of the screw when seated as well as a finishing treatment upon completion of the fastening against a fastened member are improved. The head part is comprised of an upper large diameter part formed with a first seat surface of inverse truncated cone shape having an outer circumference of a curved concave surface and a small diameter part formed with a second seat surface of an inverse truncated cone shape concentrically and integrally connected to a lower part of the large diameter part and having its outer circumference of a curved concave surface, and an annular projecting edge is formed at a connection part between the seated surfaces of the two-stage curved concave surfaces.

Abstract: By modifying a shape of a head part of a screw, an inserting performance when a punching operation is carried out, a fastening performance when the screw is seated, and a finishing process upon completion of fastening against a member to be fastened are improved.A seat surface of the head part is formed in an inverse truncated conical shape with its outer circumference being a curved concave surface and the upper surface of the head part is formed with a spherical concave surface. The head part is provided with a plurality of spot facing projections extending from the seat surface of the small diameter part at the lower portion of the head part adjacent to the screw shaft part along the curved concave surface of the seat surface in a longitudinal direction. The upper surface of the head part formed in the spherical concave surface is provided with chamfered portions in which an opening edge of the engaging groove of a cross-shaped hole is cut in a conical shape.

Abstract: A shape of the head part of the screw is improved and performance of insertion of the screw when punched and performance of fastening of the screw when seated as well as a finishing treatment upon completion of the fastening against a fastened member are improved.The head part is made such that the upper surface having an engaging groove to with which a screw driver tool is engaged has a spherical surface, and the head part is comprised of an upper large diameter part formed with a first seat surface of inverse truncated cone shape having an outer circumference of a curved concave surface and a small diameter part formed with a second seat surface of an inverse truncated cone shape concentrically and integrally connecteed to a lower part of the large diameter part and having its outer circumference of a curved concave surface, and an annular projecting edge is formed at a connection part between the seated surfaces of the two-stage curved concave surfaces.