Well I hate to ask a DUMB question.
What is the size and the TPI Size 7/16th and the thread count of 14 TpI or 16 TPI?
I know some one is going to ask where did he come from?
It's a really odd size, so it isn't a stupid question.
13/32"-16 tpi will work, but here's a thread where one guy says the thread actually was a then used standard thread called #26-16 with 0.398" diameter, so 13/32=0.406" is close enough?
Bill: If you need a set I have plenty of them including the open spool and nuts.
There are two head sizes on those. The early ones are 5/8". The late ones are 9/16", which is way easier to put a wrench on.
If you have the open spool type there is only one size nut ie 5/8. Larry is correct on the closed type the 9/16 is much easier to get a socket on and is the only one I will use. I even some times use the 9/16 on the open spool because its is so much easier to use my air ratchet. Any way I have all three types if you need them.