Alright everyone, I've never seen a rivet like this before & have called a few rivet specialty places & they were not able to identify it either. I apologize for the picture quality; it's blown up a touch to show the detail. The actual size of the rivet head is about 5/16". The head appears to have 2 sections (the main one is a little worn on this one) and then on the inside there appears to be a very small square drive down inside? Anyone recognize what it is? It almost looks like it might be removable?? I cant find any square drives that fit it, it's quite small. Take a look...