Technical Flathead 8BA Offenhauser 1075 intake manifold

Hi!

I'm installing an Offenhauser 1075 dual intake manifold.
Now I'm stuck at the threaded hole under the rear carburetor.
I have left over an air vent line from the gas tank, as I think it is.
What size does the thread have? Is it unf or unc?

Thanks for help!

 

Vacuum fitting goes there, for the wipers.
Probably is 3/8"- 24 thread (fine) or 1/8" pipe thread. Just use a short bolt to plug it if not needed.

 

Would be nice if somebody knew exactly as inch threads are not common in Germany and I have to order all online. I hate it to wait just for a fucking screw
Thank you guys!
In that short time I‘m in this forum I got good help! Would have saved me lots of Dollares if I would have joined earlier. Seems like Flatheads are eating $$$

 

Jonesi - I went to the garage & checked an Edelbrock & Weiand intake, don't have an Offy.
3/8"- 24 thread works. A short (1/2") long bolt with a thread sealer would work .
Flatheads eat a lot of money, but older Cadillac's are not far behind in cost.

 

Now I know, it’s the vacuum for the brake booster

 

Some of the 8ba's had a vacuum dizzy as well.