this invention relates to an improvement in an extruder with two press screws arranged coaxially in one another in an outer jacket and each carrying a screw thread for feeding various plastic materials , for example , granulated soap , to the press nozzle , where the outer screw is driven while the inner screw is stationary , and where the inner screw is in communication with the charging material in the area of the charging hopper through window - type openings in the outer screw . the said improvement involves a mixing element between the end of the press screws and the extrusion nozzle whereby the two strands being extruded are mixed .