I based this design from other designs i saw on PrusaPrinters. I like the design but I needed something bigger for my project. So, I designed my own. Fusion 360 even said this was Over-engineered, so this should hold nearly anything (within reason). I used 10% infill .3mm layer height in Prusament PETG.

THERE IS A LATTER B ON EACH BRACKET, TO INDICATE BOTTOM OF BRACKET!!

These are designed to hold IKEA BURHULT SHELVES (or of equal thickness)

(the orange was V1, yes i know the mistake i made, the black is V2, which is perfected.