If it didn't have the scoops on the bottom i would be confused, but as it stands it just makes logical sense.  I do wonder what the limitations are though.<br><br>From how i understand it, its the scoops at the bottom that are forcing new material into the tube, and around the screw.  Meaning that the higher the tube, the more back pressure there will be on those scoops, limiting its maximum height for a given material.<br><br>In a regular screw design surely the screw itself is performing the lifting mechanism, so the pressure will only be the small amount of material on each section of the screw, meaning the height limit should, in theory be far greater.