A filament guide that screws e.g. to the top bar of a 2020 beam used for direct drive extruders where the filament spool is beside or below the printer, to guide it from above.
The distance from the outer edge of the 2020 beam to the center of the wheel is 50 mm.

Easy to print!
No supports needed.

The wheel and key are a tight fit.
Use sand paper or scale print slightly if needed.

Installation: Push the wheel on to a 6800 bearing (10x19x5 mm), push pin into the bearing (flat side of the wheel facing outwards) then carefully push the key/retainer into the slots until you hear two clicks.
The assembly is then screwed from the bottom of the top beam using an M4x8 screw and T-nut.

The retainer can be moved so filament can be inserted from the side, but cannot escape on its own.