A quick learner from Port Orange, Florida says:
November 28, 2014
Will these work on a 4 inch thick wood mantel?
Dave from SWISCO responded:
December 2, 2014
Hmm... I'm not sure about a 4" thickness. It might work, but you have to keep in mind that this part works best when the top triangular head lays flat on the mantle. With a 4" thickness you would have to stretch the hook to ensure that, which may affect its strength.