Flywheel nut size

[Johngoat2002]

I have recently bought a 1960 evinrude lark 2 for price I couldn't pass up. It looks like someone has taken it apart to replace a magneto. Once a few new parts were ordered I noticed that the flywheel nut threads were damaged. Can anyone tell me what the thread size of this nut would be so I do t have to buy a $25 oem nut that would normally cost .75 at a hardware store. Thanks for the help in advance.

 

[F_R]

9/16-18. But it is thinner than a "normal" nut. Actually called a "jam" nut, although it isn't used for that purpose here.