I had two problems: it's a shame to throw away 3D printer filament spools, and buying copper wire by the meter doesn't come with spools, which you have to pay for. It's very inconvenient to unroll wires from a spool. And if you put a wires on a spool of the wrong size and try to rewind it, everything gets tangled. So I made this spool that can change size. It's basically a Longworth Chuck. It's completely customizable; you can simply change the dimensions—the outer diameter, the inner diameter, the thickness, and so on—to suit your needs. I used M6 bolts for the adjustable jaws.
Example how it works: