Abstract: An extruder for plastic materials wherein an end portion of the extruder screw extends from the extrusion cylinder and is coupled to the adjacent end portion of the drive shaft by a U-shaped coupling element which partially surrounds the two end portions and by a claw-shaped coupling element which overlies flats on the end portions of the extruder screw and drive shaft and is secured to the U-shaped coupling element by a screw. The flat on the end portion of the extruder screw is inclined with reference to the axis of the extruder screw if the shaft is to transmit torque to and to reciprocate the extruder screw. A U-shaped clamping device is used to secure the U-shaped coupling element to the end portion of the shaft.