Abstract: A variation device of the present application includes a shaft (A) on which there are assembled spacing rolls movable axially if submitted to an axial thrust. In a preferred embodiment, the device includes two combs located around the shaft with a 180° spacing, suitable for making, by the automatic control of a pneumatic piston, traverses for approaching to and moving away with respect to the shaft and each comb is provided with a plurality of forks suitable to make, using the automatic control of related electric motors (M1 . . . M8 and M1? . . . M8?). Independent axial traverses, in a direction suitable to drag and position the rolls at the wished distance and, in the opposed direction, for being brought again to the rest position. The automatic intervention of control means for combs and forks is coordinated by an electronic apparatus running according to prefixed programs.