I wanted an easy way to load up 50g samples of filament onto a spool without laborous winding. Basically, remove the side, drop in the hoop of filament, hook the tail end, screw the side back on.

The center is for a 8mm rod. I've enclosed CAD sources for those that want to alter it for other rod sizes.

This design assumes 0.5mm bead widths, which is good for 0.35 and 0.4mm nozzles. You shouldn't need supports but you'll want to be able to do 25mm bridges. I suggest two perimeters (any more and your slicer might give you trouble) and 4-6 top and bottom layers.

I've made this thin and light, so it's very sparing of materials. It should be less than 50g of material consumed. However, if built well, it should be durable.