Shifter ball size

Can someone tell me the thread size of the shifter ball on a Muncie transmission M-20 in my 1971.  I am going to order a custom one from a guy I met at a car show and want to make sure I get the right size insert.   I also need the thread size for a 91 six speed shifter as well.

Thanks

Neil

You might find the answer here. I'm pretty sure there is an application guide in their website someplace:

http://www.flameball.com/HomePage.htm