These brackets will support up to a 1.9 inch (~48mm) pole, pvc, or dowel. I am using a piece of 1.5" SCH40 PVC, which fits perfectly because it is 1.9" on the outside. This holds my filament spools perfectly.
Of course, you can use these with smaller diameter rods, poles, and pipes as well. The bottom cradles smaller poles so they don't move around too much.
I will update with photos when I have it mounted in it's permanent home. :)