This plate peg can easily support up to the 30 pounds and fits 2.3" x 2.3" uprights with 5/8 holes. It was designed using a topology optimization process to minimize the material used with little or no loss in strength.

You can print it the material of your choice, I printed mine in PLA+ and it works perfectly. Keep in mind that plastic is prone to creep and simple PLA might not be the best choice.