Protects the PTFE Bowden tube from catching or being cut/scarred by the Dibond on the top of the gantry.If the filament you are using is wound particularly tight the PTFE tube can curl back and drag across the top of the gantry. The sharp edge of the Dibond can cut groves into the soft plastic tubing and cause it to catch while printing.Print 2 of these and slide them onto the top edge between the mounts for the Z-axis smooth rods.