Bookcase Shelf Peg/Pin

You know those little nubs that hold up loose shelves in cheaper bookcases? These are those. I think I've lost a dozen of these in my lifetime, and each time the shelf is always left awkwardly balancing or using a random tall object as a makeshift bracket.

The ones here I tried on my different cabinet and shelves and it seems to work on all of them, but your mileage may vary. They seem to be somewhat standardized with pretty easy going tolerances.