While there is quite a bit more to understanding the different chain variations than by just showing the skull link of each type, it's somewhat difficult to totally explain all of the characteristics in this single thread.
In Ralf's SS edged weapon reference, he certainly does and excellent job in breaking down the criteria to distinguish the differences and characteristics of each variation. We also have a shortened version of that in the blog section of our site.
I've shown the TYPE C already. Here are the other 3.
