causes the mountings 33 a 33 b 34 a 34 b and as a result the lower rollers ii and iii respectively to be displaced and moved in directions c d and e f respectively the associated upper rollers 13 and 14 are correspondingly moved in a manner not shown in directions c d and e f respectively by that means the nip line spacings between the roller combinations are modified and set locking of the sliders 35 a 35 b 36 a 36 b is accomplished by means of a catch device stopping device or the like one suitable form of stopping device being shown in fig7 referring to fig3 a the lower rollers ii and iii are driven from the right hand side of the draw frame seen in the direction of material flow a by means of a common loop mechanism in the form of toothed belt wheels 40 41 and a toothed belt 47 the different speeds of rotation of the lower rollers ii and iii are achieved by means of change gearwheels at the drive trunnions iia iiia provided with different numbers of teeth the toothed belt 47 runs in direction b that is to say contrary to the work direction onto the control.