Abstract: A mixing element for a screw extruder comprises an element including opposing lobes and a central portion having common opposing broad surfaces; one lobe broad surface being formed into a taper. The elements may be used individually or combined in blocks, with the elements of a block oriented in various combinations. The blocks may comprise two or more elements. The tapered lobes provided reduced pressure and temperature of the process as compared to prior art mixing elements. Also, more graduated control over temperature and pressure are provided according to the value of the taper magnitude, the number of elements used in a process and the relative lobe orientations in a machine.