Abstract: The material-processing machine comprises at least a screw (11) driven in rotation inside a sleeve (1) and constituted by a central driving shaft (2) on which are mounted a plurality of screw elements (3) forming a stack of adjoining elements clamped between an abutment and clamping means placed respectively at the two ends of the shaft (2). The clamping means (4, 5) are arranged in such manner as to exert on the stack of screw elements (3) a prestressing force capable of opposing the separation of the screw elements (3) from each other in operation of the machine. The invention is especially applicable to the construction of screw extruders.