This is a two piece bracket that simply drops into each corner of your rack storage unit, allowing for extra shelves. I printed mine solid to be as strong as possible, and while I'm unsure just how much load you could put on these before they fail they've been holding up great for over a year now and feel sturdy and solid.

To install a new shelf to your rack, print 4x of each model. Assembly is easy, just drop in the Under Brackets first at each corner, followed by the Over Brackets ontop.

This is a remix from a thingiverse model but for the life of me I cannot find the original model anymore so my apologies to the creator of the little nubbins that slot in, but thank you for your work!