Bookcase Hanger Bracket

This is a bracket designed to hang a filament spool from the top of my Crate & Barrel bookcase where I keep my Printrbot. It holds a captive 5/16" nut so that a bolt or threaded rod may hang down to hold something (up to a few lbs max). It is designed to slide over the edge of the case and be held only by friction so I could avoid drilling holes in the wood.

The bracket height is about 1 37/64".

NOTE: This design is for the bracket on the left, and I've cleaned it up slightly from the on