Prusa MK4 MMU3 PTFE Straightener

The tube coming from the MMU3 to the top of the extruder on the MK4 (or MK4S) gets bent.  Sometime the filament getting sent down from the MMU3 will catch on the edge of the Festo QSM-M5-4.  This model makes sure that the PTFE tube is straight for a short distance going into the fitting.  I know the filament was catching on the fitting at the MMU3 because I could hear the gears skipping trying to push the filament and see the tube jumping.  If I straightened the tube by hand the filament would move into the tube properly.  I'm not sure that one is needed on the extruder side of the tube but I have seen it catch going into that as well so I put one there as too.

I printed this on a Prusa MK4 with eSun+ PLA (but any PLA or PETG should work fine).  I used 0.15mm layer height with a 0.4mm nozzle.  The Festo fitting goes into the bottom piece with the threads pushing out the bottom. There is a hex section at the bottom to accept the fitting. The four screws (probably overkill) are M2.5x8 and thread directly into the plastic so don't torque too much.