I needed small spools for my coaxial cable and dipole antennas that could fit inside standard .50 ammo cans.  Couldn't find anything comercially available, and then I remembered I have a 3d printer, so I knocked this out in tinkercad in about an hour.

It's a symmetrical design, so the idea being you just print two of objects 1 and 3 and screw them together with standard M3x20mm screws.

File 2 is a small bracket that can be used to affix the spool to other objects.

File 4 is a small knob that can be optionally added to use to spin the spool as you wind whatever onto it.