Made these for a shelf I built for my daughter. The shelf was made using reclaimed melamine particle board and 12 mm rebar. I welded the rebar construction and painted it white. Then secured the rebar to the melamine board. I also added an angle to secure the shelf to the wall. The lower and upper clips is different to make it easier to slide the intended boxes in the "compartments". They look like giant cable clips!

UPDATE: Added clips for 10 mm rebar (for the upper shelves).