An arrangement including two conveyor screws which are arranged rotatably moveably relative to each other for processing a pasty material like a foodstuff product or the like, having a first conveyor screw and a second conveyor screw which have interengaging helical flights and which in particular are drivable in opposite relationship. The conveyor screws are of different size diameters and/or the conveyor screws have a different number of flights. In addition, the surfaces of the interengaging flights are so shaped and matched to each other that they are in contact with each other along a substantially continuous contact line extending substantially in the longitudinal direction of both conveyor screws to hinder, preferably prevent a return flow of the pasty material.