"Richard J Kinch" wrote in message
...
Paul K. Dickman writes:

I suspect that just about anything with 27 tpi evolved from gas piping.

Sure, but that just defers the questions as to why 27 at all? Market
manipulation?

Gas lighting was starting to spread while Maudslay was still inventing the
screwcutting lathe.

My personal guess is that 27tpi is as fine a thread that men can reliably
chase freehand.

Paul K. Dickman