Abstract: A plastic screw anchor having legs each formed with a recess which provides the leg with good flexibility whereby the legs can easily deform during the insertion thereof into an aperture of a supporting plate and also provides a strong grip between the screw anchor and the supporting plate. A wing integrally formed on each leg prevents the screw anchor from coming out of the aperture after having once been inserted therein.

Abstract: A pierce nut has a plurality of projections which are integrally formed with a cylindrical body of the pierce nut. When the pierce nut is pressed against a metal sheet laid on a back-up die, an opening is formed in the metal sheet only by shearing force between the pierce nut and the back-up die, with no other force being used to press-break the metal sheet, and the projections are deformed by an annular bank portion of the back-up die at different portions thereof each time the back-up die is used. Thus, the use of the present pierce nut in combination with the present back-up die remarkably extends the life of the back-up die.

Abstract: A tapping screw in which a shank includes a main shank portion having a substantially uniform diameter and a reduced diameter shank portion having a substantially rounded triangle shaped cross-section. Tapping is carried out by the apexes of the rounded triangle in the reduced diameter shank portion, and therefore, screwing torque is greatly reduced as well as the fastening force is greatly increased as compared with a conventional tapping screw.

Abstract: An upset bolt provided with a pressure formed recess on the bolt head. The recess is formed by the combination of three separate surfaces, that is, concave, convex and flat standing surfaces which respectively form lower, middle and upper portions of the recess. By virture of provision of the concave and convex surfaces respectively in lower and middle portions of the recess, stress concentration occurs in the region along the concave and concave surfaces when the recess is pressure formed. Since the region of stress concentration is positioned away from the neck portion of the bolt body, the breaking strength is remarkably increased as compared with conventional upset bolt in which the stress concentration occurs in a region near the neck portion of the bolt body.