The filament guide is put on the same bar where the spools are mounted. (diameter of 19 mm)

The guide allows to fit in a PTFE tube. 

It was created as the filament on my spools was entangling while printing. 

I added the blender file in case you want to change something.

I used PLA with a 0.4 nozzle. It was printed with a MK4 MMU3 printer. I used brim, but I don't think it was really required. Printing time about 34 min.

Feel free to use.