I have designed two tipes of forelok: one whith a lip to handle it more easily and one without lip if you haven't space near the extruder motor. This shrewdness decreases the bowden movements and it improves the qualiti of the print. Before this i usually used 5.5mm for retraction, and naw i use 3.3mm. It's a good sesult ! I advise you to use this obgect if you have a bowden 3dprinter ... prosecutour improvements !