Spool Holder for Modular Shelving Unit

I had made up some smaller brackets to mount on the inside of the shelving unit some time ago (included) but decided I would like the spool to sit outside due to convenience.
I tested with 2 clips and it seemed more than strong enough with the frame bending before the bracket suffered any noticeable effects. The cut out is to allow it to fit over the shelf which protrude but it doesn't require it to be placed over the shelf section.
The brackets could also be mounted to the inside of the shelv