Came across this screw thread chart, I couldn't find a link to it doing a forum search and thought it may be of some use when dealing with unknown threads- it lists quite a few different watch threads you just need to pick through the list to find them. It also lists a lot of what I would call oddball threads, the type that you might come across once every 10 yrs.
http://pages.cs.wisc.edu/~bolo/workshop/thread.html