Do you need a simple way to hold a spool of 3D printing filament while printing? A common 12″ bar clamp will do the trick for many workspaces. Just clamp it to your work bench so that the bar is parallel with the ground and slip the spool over the remaining bar. You can use a piece of filament through the hole on the end or a clamp (as shown in the photo) to keep the spool from walking off the end of the bar.
To reduce the friction on the spool, I printed a small tube that I put over the bar so the spool rests on the tube instead of the rectangular bar but, honestly, I don’t see that it makes much difference.