To guide your filament down to the print head.

The most efficient and simplest solution.

It's designed for my personal filament reel holder solution - a small shelf directly above the MK3s.  Having the reel above the printer reduces drag, vibration and noise. The reel itself is on rollers -see my Filament Roller at https://www.printables.com/model/305811-filament-roller

There are two versions of this model each with g-codes for PLA and PETG (which is why there are so may files for such an incy-wincy thing.

I recommend using PETG as PLA is more brittle and may snap.  You could also use Nylon (v3 only cause you can't stick nylon to anything) or whatever else that has some flexibility.

Version 2 (files with ‘v2’ in their names) is solid designed to be attached to the shelf with 2-part epoxy.

Version 3 (files with ‘v3’ in their names) has a 4.2mm hole beveled for a countersunk screw.

They each take less than 0.6M of filament.

Version 1 - the gap was too wide and the filament kept escaping.  Naughty, unruly filament. Rather - naughty, unruly design.

Hardly need mention it but once attached to the shelf the round bit is pulled out to allow the filament to be inserted/removed.

Regards, Paul