Image: Colleen & Eric
Here is another instance of a wing nut being put to good use in design.  

From Colleen & Eric, this cubed wing nut bookend can be moved into place along a notch in the wooden shelf and secured as needed.  The bookend is made of powder-coated aluminium and the bookshelf is offered in Beech, Walnut and Oak. 

Images: Colleen & Eric