Despite all the filament clips out there, none seemed to work well for me - either they pop off the spool rim, are hard to thread the filament through, or allow the filament to slide out.
This is clip will tightly and independently grip two strands of filament. If toleranced and printed properly, the filament will "click" into place and not slip, even for glossy filament.
This prints well in PLA and uses only a few cm of filament per clip.
The customizer should allow for any size filament, but I have not tested anything other 1.75mm.
UPDATE 12/16/17: Changed OpenSCAD model to avoid "coincident faces" issues in preview and any possible non-manifold objects. Regenerated STL files, but no functional change.
PLA works great, nice and stiff. PETG might be OK too, I did not try yet. Since object is so small, print 6 or more up at once to give the layers time to set.
Make sure the Z "seam" is not inside of the clip face, which is the default in Cura and probably other slicers. If it is, it will cause interference and prevent the filament from snapping in fully..
In Cura 3, I recommend setting "Seam Corner Preference" to "Expose Seam" to avoid this.
I also use "Horizontal Offset" set to -0.05mm in Cura as this renders truer diameters on holes for me. If you don't then add "-0.05" to the offset for a more negative value in the customizer.
The above will get you started, but you may need to tweak for your printer and slicer.
Make sure throat of clips is free from stray filament threads (boogers).
Clips should snap firmly and audibly onto filament, and not slide easily.
If filament slides out, make "offset" value more negative in 0.05 increments until snug. If clip is too hard to install, make "offset" more positive in 0.05 increments.