I love those metal wire shelf with the 1" rod and rings. However, extra shelf are usually hard/expensive to source.

So this is a bracket to mount your favorite plank of wood or what have you instead.

Just slide it over the stock 2 piece round clip, rip your plywood to suit and fasten with screws.

Rip a +/- 30x30mm corner on your plywood for a seamless fit around the posts (not necessary for top shelf)

I used half inch & 3/4 inch plywood and printed with PETG for max strength and longevity. PLA should be fine also.