Temporary PTFE Coupler (Prusa MMU

thingiverse

I find that when I've got filament from one PTFE, and feed it into a second one, after the print gets going these can bump together and cause friction issues. This is a simple part to let your PTFE have something solid and square to hit against without restricting filament travel. To avoid this problem, I use a heat-set nut so that the coupler can thread onto the existing PTFE that connects the MMU to the Mk3's extruder.