a polymer - extruder screw has a mixing section with relatively deep channels between flight lands at a proximal end , progressively shallower channels with a progressively larger screw core of a central transition section , and finally a metering section having a plurality of at least three pressure channels juxtaposed helically between flight lands having channel interruptions comprised of helical inclines and constant - radii tops in helical progression to a distal end of the extruder screw where the pressure channels end with equal depth at an interface with a metering gate of an extruder . the pressure channels can be symmetrical or asymmetrical in angles of incline and decline at opposite helical sides of the channel interruptions for optimizing channel depths , for positioning of maximum channel depths in relation to tops of channel interruptions , for equalizing channel depths at the distal end of the extruder screw and for optimizing incline and decline advantages for polymers with different characteristics . helical degrees of channel - interruption cycles can be different for different polymers . the screw core in the mixing section can be graduated in diameter and distance between flight lands can be designed as required for different polymers .