I saw it on a folding table I'm planning on copying.. It looks pretty thick- see the couple pictures below;
Cheers guys and gals!
I know it as a butler's tray hinge, or drop-leaf hinge.
I believe it's called a leaf hinge.
Butlers hinge because they are usually found on the serving tray that your butler would serve tea and Twinkies on. The hinges are unique in that they allow the edges of the tray when folded down to be flush with the tray surface.
Woodcraft has them. They call them table hinges.