I don't get the difference. Wouldn't the relative motion of sand, pipe and screw be the exact same wether you rotate one or the other? Number of support points for screw and pipe remain the same... Am I missing something?,(reply>), The real trick I think to it seems to be in the larger gap between the screw and cylinder wall. It makes the flow more constant and doesn’t require syncing a loader to it. Plus there’s no rotation bearings/seals at the base of the screw.