1939 Temp gauge fitting

[47Merc]

I am looking to fit a mechanical temperature gauge in a 1939 Tudor with a 59A motor.
Can any one tell me what size / thread the bush is that the sender unit screws into and what size the thread into the head is. Also where I could possibly buy one. Thanks.

 

[deuce lover]

John Wolf & Co in OH and ThirdGen Auto in TN has those. Southside Obsolete in MN might also. Head thread is 1/4 NPT, gauge nut for the bulb is 5/8 X 18.Here is a link to one that sold recently.
https://www.ebay.com/itm/154506625937?hash=item23f9500391:g:HPMAAOSwbytgp~tP

 

[marko39]

aftermarket temp gauges usually come with more than one fitting. thats where i got mine for my 39.