This is a basic spool holder I designed in Sketchup, after seeing some of the other spool holders here. My version is very simplistic, being just a triangle style frame held together by 1/4" wooden dowels.

You'll need a wire or rope spool from a hardware store, or another type of spool to utilize this holder. I am designing a printable spool that will be compatible with this holder, which I will add to this thing when I have it finished.

The horizontal holes do have a bit of an 'unsupported overhang' at the top, however mine printed without any issues (as you can see in the image). Your mileage may vary ;-).

Print 2 of each piece (top, footA, and footB). Use 1/4" wooden dowels to connect the pieces together. You'll need 6 equal sections for the sides, 2 equal sections for the front and back, and one slightly longer piece for the top.

For my setup I used the following lengths:

Sides (x6) : 240mm
Front/Back (x2): 230mm
Top (x1) : 255mm