This is a reusable and adjustable spool to be used with spoolless filament like this one: https://www.dasfilament.de/filament-refill/pla-1-75-mm/
The part was designed with the target in mind to use as little material as possible while not letting the spool get to small or unstable. I also wanted the spool to be a bit more sturdy (hence the screws) and not just plug it together.
I made the spool adjustable so it would be compatible with different filament brands. But since I haven't used filament refills from another brand than dasfilament yet, I don't know whether different brands use different inner diameters for their spools. :)
You need 6 M3x10 screws and 6 square M3 nuts to assemble and adjust the spool. To assemble the spool, the parts have to be printed in the following quantities:
The diameter of the inner ring can be adjusted by loosening the screws, sliding the inside-parts in the desired position, and retightening the screws.
For the first assembly, screw one outside-part and three inside-parts together, but do not tighten the screws yet. To protect the other parts, the screw caps or a washer should be used between the screw head and the parts. Place the spool on a table with the outside part facing the table. Now, place the filament on top of the spool and adjust the inside-parts to the inner diameter of the filament you are using. Then, carefully place the remaining outside-part on the top and tighten the screws. Turn the spool around and tighten the screws on the other side.
Changing the filament requires you to loosen the 3 screws on one side, remove the "outside-part", replace the filament, put the outside-part back in place, and retighten the screws.
It takes about one minute with an electric screwdriver, but I am sure there are better and easier designs out there. However, I'm using three of them for over a year now and have no complaints.