The distribution of load stresses on the engaged threads of a standard screw or nut is not even. Indeed, the first engaged threads bear a large majority of the load. Consequently, if the load is too great, the threads break and the function is not provided anymore by the screw or nut. The prior art describes threads having a depth or a pitch that vary substantially in order to induce self-tightening. The aim of the invention is to optimise the mechanical resistance and fatigue resistance of the screws via a better distribution of the load on the threads thereof and without inducing said self-tightening. It has been demonstrated that the control of the pitch variation, within a predetermined pitch range, makes it possible to control the distribution of the stresses on the threads. It is possible to determine a different variation corresponding to each load case encountered.