When I got my 40, the steering wheel was so stripped, (on the shaft), that there was really no threads left and the wheel was pretty much moving on its own without turning the shaft, (Scary).
I used what I had and fixed it.
I only had an american tap/die set, so I cut new threads 3/8x24 and put a new "nylock" nut with a liberal amount of red locktite.
I was surprised to see that the end of the shaft, (threaded part), was so short. There was not even enough length to add any washers. Seems to me this is something you do not want to come un-done.
I cant believe that mine was being driven as it was. I think that the only thing holding on the wheel and helping it to "move" the shaft, was the pressure from the cushy center pad of the wheel itself, (being held on with the 3 small screws at the spokes).
With the amount of damaged and or sheared off material from the threads, I dont think I could have repaired the existing threads, going to american on that was a good option as I saw it...at least there was some material to cut and lay some good new threads, (the 3/8x24 was a tad smaller dia.). Still I am not sure what original thread measures.