On Nov 30, 6:22*pm, "Karl Townsend"
wrote:

I learned something today. Don't happen often for an old goat like me. Is
this just some sort of emperical formula or is there a logical basis?

Karl

Both. plus politics:

http://www.sizes.com/tools/thread_history.htm

http://www.sizes.com/tools/thread_american.htm
Scroll down to History.

The inch was redefined as 25.4000000000mm too.

jsw