I have some of the wire shelves that use half-round rings to lock the shelf on the posts. I lost some in a move. I printed these as an emergency part so I could put them together until I found the correct ones.
jrclem has a much finer version that's truer to the original....http://www.thingiverse.com/thing:1583164
Only benefit is mine is streamlined to nest them together standing up (so you can print a bunch quickly)