Abstract: A self-tapping screw includes a head and a shank extending from the head. The shank includes a cylindrical shank immediately below the head and a truncated conical shank following an end of the cylindrical shank. The cylindrical shank is provided with a plurality of first external threads, the truncated conical shank is provided with a plurality of second external threads following the first external threads, and a peak of each of the second external threads is provided with a biting surface having a concave-convex form.

Abstract: A screw has a head with a cross-shaped groove having first to fourth wing grooves, each having bilaterally-formed inner side faces defined by opposing base-end inner side faces, opposing intermediate inner side faces and opposing distal-end inner side faces angled at angles relative to each other so that the first angle of the base-end inner side face<the second angle of the intermediate inner side face<the third angle of the distal-end inner side face. The base-end inner side faces define a trapezoidal base, the distal-end inner side faces define an inverse-trapezoidal distal-end groove, and the intermediate inner side faces define an approximately parallel intermediate groove between each base-end groove and each distal-end groove. Each of the inner side faces is provided with an elevation angle spreading toward an opening face of the cross-shaped groove.

Abstract: Structure for screwing on sheet metal an object having a fitting hole comprises sheet metal having a prepared hole formed therein in the shape of a saucer and also having a saucer-shaped lip which has a thickness equal to the thickness of the sheet metal and defines the prepared hole, and a screw composed of a screwhead, a shank depending from the screwhead, external threads formed around the shank and a substantially conical tip. The screw is passed through the fitting hole in the object and driven into the prepared hole in the sheet metal while catching the leading end of the saucer-shaped lip between the adjacent external threads.

Abstract: A method of making a screw for forming internal threads in a hole in a work formed from a blank having a shank portion and a frusto-conical shaft portion. Three flat portions extending parallel with the axis of the blank are formed on the shank. A length of the end portion of the frusto-conical shaft portion is left as right circular. A delta formed region is formed on the head end of each flat portion, and has a peripherally arcular convex surface and tapers to the flat portion. By thread rolling all but the shaft end portion, spoon-like recesses are formed at the crest of the threads passing on the flat portion to form inducing male threads. The depth of the spoon-like recesses sequentially decrease on the delta formed region to produce transient torque increasing characteristics.