Thanks but i dont understand what you say... "variant in the thread" and "fine vs. course"... what are you trying to say?
If you look at a screw/bolt, it has threads, right? There's a specification as to how many threads per X are on the fastener, more = fine, less = course (more or less), i.e., just because you match the diameter spec (M8 or 5/16") doesn't necessarily mean it will work.
My recommendation: take the part you're trying to match to a hardware store where they sell fasteners, and test for proper fitment.