I made this Rack bracket to allow my round storage tubs to be put on the rack as the others I found are to close to the wall so doesn't allow the tub to sit properly, I also made a small support for the round filament storage tubs so they sit straight on the rack.

The rack needs 21mm dowel, I only used 2 brackets will no issues spaced approx. 1mtr apart, but 3 can be used if you want the additional support.

220mm in length to allow for the round filament tubs, the tubs I use for filament storage have a 240mm lid and the bottom is 215mm. the dowl are space 151mm apart so you can also just put 200mm spools on it if you don't use storage tubs.

I printed them in PTEG but PLA will be fine.