A very simple printable reverse bowden adapter for the MK4, it doesn't need support if you print it as shown in the provided .gcode. I recommend using 0.1 mm layer height so that the threads are smooth.
I designed this to work well with my MK4 X-axis bracket, which also takes a PTFE tube with an outer diameter of 4 mm.
This way the only thing you need to set up a reverse bowden system on your MK4 is a PTFE tube, and these two printed parts.
The author marked this model as their own original creation.