In-spool 1.75mm filament clip.
I tested 10+ clips and didn't like any of them. Received something similar on a spool of Solutech filament I purchased - theirs were more difficult to handle due to their overall smaller size, so I thought I would design my own clip modeled after their basic design but larger (after the fact, I also found a couple of similar clips here on Thingiverse). Therefore, I do not claim this is an original design even though it is proving to be quite popular.
I like that it sets inside the spool and does not clip to the edge. Simply unrap one layer to attach the clip, wrap filement around again and attach. When in position, push filament down to secure. These are the absolute easiest on/off clips I've used.
Simple, but elegant solution. The only think you have to remember is to uninstall it when mounting the spool (I've forgotten a couple of times, but clip managed to pop off on its own during filament feed).
Print in orientation provided (looks like the letter "M" when looking down on the top of it), and feel free to multiply (I typically print 12 at a time).
This is designed for 1.75mm filament.