There are special nuts expecially around a forum like this one.
The only different types of nuts I've known are the stretchy types and solid ones or was that bolts?
Anyway one can stretch with stress and not come off the other will just come off or crack? Still think that applies to the bolts not nuts.... though?
Mate that looks like a plain nut to me LOL! Get the nut from other side off, then go to the nut shop for comparision you can compare your nuts together