Steering wheel nut thread & size

You need to figure out thread pitch (threads per inch) I'd bet it is SAE meaning "fine thread". It will NOT be course but it might be "special.

If you don't have a thread gauge, you can press a piece of paper against the threads, and capture the "fingerprint" of as many as you can. Use a good rule and magnifier to count threads and figure how many per inch. 17 per half inch, etc is 34 TPI