How to tell between Type II, III or IV hitch?
 

Trying to identify the class or type of towing hitch on my Runner. What are some of the signs between the types/classes? I think I have either a type III or IV...

This should help:
http://www.hitches4less.com/trailer-hitch-classes.html

If it came factory, most 4runners have a class III hitch.

There should be stamped into it somewhere both the class and the trailer weight/tongue weight. You can't tell just by looking at them - (although you would not likely confuse a class 1 with a class IV...) Unlikely anyone ever made a class IV for a 4Runner, if it's a frame mount it's likely a class II or III.