I ran across an odd size thread today, on the 1925 Elto Lightwin, model C,
on the water outlet tube that goes thru the exhaust manifold.
I had no tap or die for this one.
The thread OD measured .388, and it has 27 TPI.
I didn’t even know my thread gauge has 27 tpi, let
alone hear of that thread.
Prepare to be boarded!