These come in 3 parts and the top piece literally just lays on the two side pieces (there is a little latch that is 100% not secure-it can still lift of super easy.  If your shelf isn't the exact measurement that the little shelf holders are then the shelf leans to the side and is completely flimsy and unreliable.  I have no perfect size shelf to try them on so I can't say for sure if they work well on that size shelf.