Ok the plugs I have that fit Model A's and T overheads a 8-32 thread but the plugs for my T are close but not the same. I can't seem to find the correct tap and with out having a plug in hand I thought someone here migjt6know what it is. It is not 88'33-32 or 1/4-20 or 28
Model T plugs are 1/2 NPT.
Model A plugs are 7/8. Are you asking about the threads at the connection to the plug wires for the terminal screw or the hole in the head? The hole in a stock Model T are 1/2 inch pipe thread.
Terminal threads are either 8x32 or 1x.7mm depending on brand of plug. I get mine from restorationstuff.com
"What is the thread for"...It is for asking questions on the Model T Forum!
Terminal end. Making my own nuts and though there 36 threads to the inch and I found on a listing of taps an 8-36 I could not find one6i in any of my taps. I do have a 4-.7 mm and will check that out. To cheap to pay t bucks ea. for new brass repos.
Also 8-32 is not the correct thread for Model T plugs. Model A yes.
See if #8-36 UNF is available.
I checked MSC and it's not even listed.
T's are 1/2" pipe thread.
I found that out 50 years ago cleaning out the plug holes for some new Blue Crown plugs.
My Pop had a Montgomery Ward pipe tap and die set we used on the farm and that was the one that worked.
4mm x .7 is the correct thread for the top of the plug. I was able to re-thread some brass nuts that were tapped 8-32. 4mm is just a few thousands larger and just enough meat to go larger. The thread also is the same for motorcycle plugs I had around, maybe even a plug for a mower.