After you get it cleaned, you can put the penetrating oil on the outside and put about 3/8 inch inside, to soak out into the threads from the inside....
That is the US M1 37mm antiaircraft gun. It is very rare. No more than a dozen remain in the world. It was used in the M15 AAA halftrack. I know one...
Have acquired this incomplete 3” Stokes mortar which I’m intending to restore and complete with other parts I have. Could anyone who has successfully...