The stands fits perfect on the build plate

I made this with aluminum tubing. found these at a local store (Ø13 thickness 1.5mm)
I added the step files so that you can easily change this to the diameter that you can find or order (or use step file to redesign, feel free)

i added 2 versions of the middle stand:
I wanted the rack to be symmetrical, this requires support.
I have added a version of the middle support that does not require support.

the side stands do not need any support (the holes can be done with bridging)

also added the 3MF file

this design fits for all spools with a diameter of 300mm