I really didn't get the benefit of rotating the outer casing instead of the inner screw. Did I miss something here?<br>And as you said, from a physics standpoint it's exactly the same, but rotating pipefittings sound more complicated to me than a simple through hole for an axle...,(reply>), If the tube rotates, the bearings can be outside of the tube and completely separated from the bulk material. Therefore you don't have to worry about sealing them bearings again dust and particles, and you don't have to worry about getting grease or oil in the bulk material.