I read through several discussion on this topic at SMC, and consequently discovered the Rockler and LV hardware option. I have a few question about the strength. I am planning on replacing the existing fireplace mantle with a floating shelf. It will be about 4" thick, 10" deep and 70" wide. The construction will be your typical torsion box. Considering this is slightly bigger than your typical display shelf, I am not sure the LV hardware is appropriate. With the 4" thickness I think I can get away with french cleats but the depth of the mantle makes me queasy. I have used french cleats to hang cabinets and it works great for that purpose, mainly because there is a lot of vertical force in a cabinet, in case of a shelf most of the force will be torsional (pulling) for which the french cleat is not ideal. I was thinking something like the picture below

free-floating-shelves-3.jpg

The question is will screws drilled into endgrain be strong enough to hold 30-40 pounds of weight. I suspect some of my wife's prized glass collection might go on this and any "accidents" will have serious implications for my fledgling hobby .