Prusa MK4 filament runout guide with PTFE fitting
A guide arm that bolts to the top of the Prusa MK4 or MK3.9 frame and routes filament from the spool holder into the Nextruder through a short length of PTFE tube, smoothing the path and stopping the strand from dragging across the frame. The bracket fits the 30 mm extrusion with an M3 T-nut slot on 20 mm spacing, rises 60 mm above the frame and ends in a hole threaded for a PC4-M6 pneumatic fitting; a 4.2 mm bore accepts 4 mm OD PTFE for 1.75 mm filament. Print it upright in PETG with 4 perimeters and a small support under the arm.
Community guides are tuned to one spool holder position. In SpeakCAD you describe where your spool sits, preview the arm in the browser without paying, adjust the height or angle in the chat, and download the STL.
Design a filament guide bracket with a 40 by 30 mm base 5 mm thick and two M3 slots 20 mm apart, a curved arm rising 60 mm and reaching 40 mm forward, ending in a 10 mm boss with a 5.5 mm hole for a PC4-M6 fitting and a 4.2 mm through bore, 4 mm arm thickness.