Abstract: The present invention is a method of forming on a fastener body by relative rotary and axial movement of a thread forming tool and the body, a thread having a pitch which changes progressively through a plurality of turns, and an apparatus for progressively deforming an elongated element having a predetermined initial cross section to the form of a coil defining an internal thread and having a progressively changing cross section giving the thread a progressively changing pitch.

Abstract: A threaded connection in which the axial load between a screw and nut in a tightened condition of the connection is distributed more uniformly between different turns of the engaged threads than in a standard threaded connection by forming one of the threaded elements, preferably the nut, to have a pitch which increases progressively as the thread advances helically in a predetermined axial direction, while the other thread desirably has a pitch which is uniform along its length. The pitch of the first thread may increase at a rate predetermined to compensate for differences in the tensile force which is applied to the screw and the compressive force applied to the nut at different points along their length when the screw and nut are tightened together to a prestressed condition.