Our polybox tubes are coming out of the lid of the box. We had a problem where the internal friction of the filament in the tube and the strength of the extruder ended up pulling on the feed tube instead of just the filament, leading to the lid being popped off by the printer. I designed this coupling piece to slide in 2020 aluminium extrusions. The polybox feed tube can be pushed in and only the filament comes out the other side. This way the tension from the extruder cannot be carried to the lid. Print vertically.