Prusament spools only have filament clips once per side per revolution. That's not helpful if the 2 sides are not aligned, and you're just a few millimetres short. But, I gotcha.
The version I got inspiration from was round… this is prusament. Also, it needed printing in PETG so the overhangs worked (stuck together) and I got messy prints. I also didn't want to cut anything.
This prints in PLA, no support, no cutting anything afterwards. Just push the pin through the spool on one of the outer holes, press a little in the middle and slide the filament into the hole. When you release the pressure, it will hold the filament against the side of the spool.
Ok, elephant in the room. You do need to have used a bit of filament for this to poke through properly. The 30-degree angle you need to feed filament in isn't quite as bad as I had thought :)
The author remixed this model.