Do as Wayne said, most tap and die sets have a thread guage with them. If you find the thread count and measure the shaft diameter that will tell you what die you need to restore the threads. If it is an 11/16, find one near you that restores old fords because they used 11/16 threads (R&L hand) on the tie rod ends. If you have a lathe or know someone that does, once you know the thread count you can set the lathe up to cut threads. On existing threads you must put the lathe in gear FIRST and then set your thread cutting tool to where it is in existing groove. If not, you'll destroy the remaining threads. I think most old time generator shops could do this for you. Good luck

Evan