U-Bracket for Doorway/Wall Spool Holder

I have my 3D printer in front of a disused door, so wanted an efficient way to store and use spools of filament. A piece of PVC pipe (20mm diameter) and this thing (x2) and it's done :-)

Easy to change/add spools, and filament flows free. If I was to do this again, I'd probably have a screw at the bottom of the "U" as well (or even exclusively) as that'd provide the most strength, but hindsight is 20/20 and this works well anyway.

Note: The screw holes are sunk for 4mm thread and 8mm head