Abstract: The joining element comprising a fastener or screw shank having a head has adjacent to said head a portion with a plurality of parallel, concentric fit-stretch rings, whose external diameter is 0.1 to 0.5 mm larger than the external diameter of the fastening thread. A fit slot is formed between in each case two rings, with a notch groove radius which is two to three times the top radius of the fastening thread. In the transition region between the head and the aforementioned portion is provided a fillet with a rounded portion having a diameter corresponding roughly to the pitch diameter of the rings and with a radius of curvature amounting to approximately to 0.1 to 0.15 times the external diameter. The rings have a stressing cross-section in the notch groove corresponding to the stressing cross-section of the fastening thread. The top width of the rings approximately corresponds to the side width of the preliminary shape of the rings.

Abstract: The screw is provided with a three-lobed thread crest, followed by a threaded portion with a three-lobed thread geometry, which passes into a threaded portion with a circular thread geometry. In all three threaded portions the flank angle of the thread is 60.degree. and the flank angle of the thread crests extending beyond the nominal diameter of the screw is 30.degree..