Here is what I used:
http://www.alliedmoulded.com/catalog...vices/p-122sc/
I got them through a local electrical supply outlet. I screwed them to the ribs, since I'm in the middle of a complete redo. The specs say 1-3/4 inches, but I ground off a little on the front and got them down to about 1-1/2, and they fit nicely behind the inner skin. Also, the front part (to the right of where the receptacle sits, flips open, so you can do your wire connections there. This is especially helpful for a GFI outlet. In any case, I wanted to get rid of those ugly "convenience" outlets where the wires are pressed into the back. Very unsafe, in my opinion.