Freighterman I think has hit the real point, which is thread friction or running torque. No point in having 3 or 33 threads showing if there is no friction between the mating surfaces of the threads. How often do you see stiff nuts reused without there efficiency being tested?. .. .If you are inspecting a joint how often do you take a spanner back off the nut and see if it has any friction? How often do you see screws hanging out of wings because anchor nuts are never replaced? How many times have you found three threads showing with the nut threadbound and the bolt loose? . .. .Surely all that the thread protrusion actually says is this bolt is through the nut and as such is a visual indicator of that fact.