OK you Model A guys, what is the radiator cap thread? It's an internal because it treads over the neck. What is the thread on the neck? checking to see if it's the same as my after market(old) radiator I have. Looking for cap options.

28-29 is an external thread. 30-31 is two flanges inside the cap that seats into two cutouts in the neck and you twist (much like a modern car radiator).

From the internet:

28-29:



30-31:

"what is the radiator cap thread?"

'28-'29 is the same thread as the gas cap.

All 28- 29 radiators I have had, had threads on the outside. My 30 looks like Ron's pic. I might have missed the real question. Tim

He is looking for diameter and thread count to compare cap size to his after market radiator. I will try and remember to check tomorrow.

1930 model pick ups did not come out until June of '30.
They just kept selling '29s and calling them '30s. so some 1930 pickups had a threaded radiator and gas caps too.

I just took my gas cap and checked it out....compared it to my rad neck and very very close but until I screw it into the cap I have I will say it looks good but still waiting to know for sure. If I had the cap here I would know but it's at the shop. So in the mean time what is the thread? I measure about 2.096" and not sure if that is some kind of pipe thread or what?

Model A 28-29 gas and radiator caps are the same threads, the only diff in them is the gas cap is vented. This has caused folks grief when they mixed them up. Aaron is right, the '29 cowl/gas tank assembly continued into the 1930 AA production for a few months, but typically those tanks had the 1/4 turn cap neck on them!! Yep, some 28-29 style gas tanks took the 30-31 cap! They are hard to find today.

Radiator neck is 2 1/4 X 18 TPI

Thanks Mark, my thinking is 2 1/4 would be 2.250" so that has thrown me off. Is it a UNC or some type of pipe thread? But thanks this has gotten me closer.