Abstract: In accordance with the invention, the breaking and stretching machines have pressure heads, each one being essentially constituted by two opposed complexes, upper and lower, each one of which includes at least two transmission chains of the Renold type which are meshed with two chain pinions (double, triple, etc) fitted on two strong parallel shafts that are supported by appropriate bearings attached to the lateral elements of the machine bedplate; those corresponding to the lower complex are fixed, while those corresponding to the upper complex are moveable, so that the latter complex may adopt, with respect to the other complex, two limiting positions; one of separation, which permits the introduction of the layer of fibres, and the other, where the elements approach one another, to be utilized during the work and in which the pressure can be adjusted.