UPDATED: 02/20/23  new model and print file.  I reversed bracket to install from front of frame instead of back.  You can just reverse the older design if you do not want to print it again by flipping the hardware 180 deg.  It will stick out further than the new design, but will still work.

This is a more well behaved spool holder.  I did this to my old TAZ machines and wonder why I took so long on my mk3's.  A lot less vibration and lateral friction.

I used Prusa black PETg, .3mm layers, 3 bottom layers, 3 top, 3 side, 15% grid infill.  Gcode included here as well.

Other required hardware is shown in photos.  Note that two spool holders can be used to have a spare spool close by.  By lengthening the allthread to about  10 inches (~510mm), you could also add a couple of fender washers and PVC spacers to add two more spools on the back of the frame.