The Prusa MK3 has some pretty narrow tolerances for clearance with things that are mounted directly to the frame and the extruder carriage.

I designed this to allow for max printing height without the print carriage running in to the filament guide. It will also prevent potential issues during calibrations. I also have remixed spool holder brackets for the Mk3 available in my designs.

Update 5/07/19: Based on feedback I've changed some angles giving additional clearance for things like the filament sensor while still remaining compatible with the spool holder. I've also added a closed loop for those that want it. I'll leave the old files as well in case anyone wants them. I also added a 2 piece version with a larger hole for those that might want it. If there are any issues with any of them let me know.