... I also have the lock. There is a special nut with a grove in that goes with lock. The other nut that came with my j hook is longer.
The J bolt has a lock for the nut to not back off. I went out and took a picture of mine. It fits into the oval recess.
I just tested the lock I have on the spare tire on my flat bed trailer and it fits! Not that anyone would take my spare, but maybe it would give me security in not thinking the J-bolt nut would back off.
