I liked mechracer84's remix of a hand guiding filament from the printer, but also keep my filament spools on a shelf above the printer and wanted a guide there too.
My shelf is 17.5mm thick, so you may want to measure and resize for your shelf.
It is just a tiny bit loose on the shelf, but a little folded paper fixed that.
I printed this upright with buildplate supports & 20% infill.
Feedback very welcome here. This is the first STL file I've (semi) created.