I know there are a lot of Top Loading Spool Holders similar to this set, but I couldn't find a set that worked exactly like I wanted it to, so I designed these. I designed them not to need any screws or other hardware, other than the cross bar (7mm threaded rod) that came with the printer.
It's designed to have the center of gravity off center, so that it will "lean" forward, holding it in place and without too much lean, so that it won't put too much pressure on the backside hook. You can use it either in a forward or reverse configuration.
After printing my brackets, I made a couple of minor changes I decided they needed; One is cosmetic and the others are functional. To make a better connection between the arms and the mounts, I filleted the connection to give it a sloped curve. Also, I increased the thickness to give them more strength. For my print the arms have a thickness of 5mm and are functioning, but I increased their thickness to 10mm. they felt like they needed it. If you think it's over-kill or you want to save plastic/time you can decrease their thickness.
Also, for staying mounted purposes, I designed them to be tight fitting. Some filing to clean up the print and open the mounts to fit the 2020 t-Slot Extruded Aluminum may be necessary.