As the viscosity of the thermoplastic material increases, it has been observed, that in single screws of the above described type, radial screw movement or wobble may develop. Clearance in the feed area between the outside diameter of the screw and the inside of the barrel permits movement of screw. As the screw wears, metal may be removed between the exterior of the screw and the inside of the barrel. This creates additional clearance which may cause even more wobble or radial movement.

Hence, it is desirable, to reduce radial movement without reducing clearance in the feed screw area which clearance is desirable for extruding higher viscosity materials. Reduction in radial movement beneficially reduces screw wear and contamination of the finished product with residual metal particles from the screw or barrel. Reduction in radial movement also helps maintain tighter tolerances between the screw and the barrel and can result in higher feed rates. Any reduction in radial movement can result in a more efficient powder feed and less wear on single screw extruders.