Joining element for two machine parts of components, such as a fit-stretch fastener and fit-stretch bolt

An axially extending fastening element for interconnecting two machine parts or components, said fastening element comprising a fit-stretch fastener having an axially elongated shank with a head at one end thereof, wherein the improvement comprises that said shank includes an axially extending section with a plurality of parallel concentric fitting rings having an outer diameter and extending around said shank with a concentric fitting groove located between and spacing each pair of adjacent said fitting rings, an axially extending fastening thread extending from at least one end of said section with the fitting rings, said fastening thread having a core forming a stressing cross-section, said fitting rings having a root diameter with a stressing cross-section defined by the root diameter within the fitting grooves and the stressing cross-section of said fitting rings equal to the stressing cross-section of the core of the fastening thread, the fitting grooves having a surface extending in the axial direction at the root thereof with at least one radius two to three times an axially extending radius defined by the fastening thread, and each said fitting ring having a crest at the outer diameter thereof with a width approximately corresponding to a width at the pitch diameter of a preliminary shape of the fitting rings of the fastening element, said fastening thread has an outside diameter and the outer diameter of the fitting rings is in the range of 0.1 to 0.5 mm larger than the outside diameter of said fastening thread.