A friend needed some simple, small, cheap spools that fitted in with the others he had for wire wrap wire. Lots of it.

Internal/usable dimensions: 30mm core. 20mm depth, 23mm width.
Two holes on each side for start/end.
The larger one has a final internal width of 36mm, hopefully.

EDIT: I would not recommend it for something like filament, it's for thin stuff. Like wire or thread.

Print two in ABS, you can get away with a single top layer, but make the core solid unless you know your printer very well.
Trim if required to get the two halves to fit(Still tweaking this bit)
Coat both sides of the centre with acetone, allow it to soak in for a few moments then add a bit more, press together, double-check alignment and apply a weight while it dries. On my spools this join was stronger than the print layers.
Tip: Rotate the two halves 180 degrees so the holes are on opposite sides.