Modular Shelf Brackets

I needed a shelf with very little depth to sit on my drafting/painting/sculpting/everything table. All shelves for purchase were fairly deep, which would take up too much of my work area.

I modeled the brackets around some cheap spruce boards I picked up at Lowes for $1.49 per 8 feet. https://www.lowes.com/pd/Spruce-Pine-Fir-Furring-Strip-Common-1-in-x-4-in-x-8-ft-Actual-0-718-in-x-3-437-in-x-8-ft/1000016907

The only dimension that matters when you buy the boards is the thickness, Lowes li