Datsun L16 intake manifold vacuum port plug size

The thread size for the L16 intake manifold vacuum port size is shown in the following picture:

The vacuum adapter shown is what is going to be replaced.

Carburetor on an l16 510 wagon

Update:
Yesterday I made my own carburetor base gasket. It didn't work. The carb has large vacuum leaks around the base. The motor doesn't drop below 1600 rpm at idle.

Update 08/14/2016:
The carburetor that I was using is a 32/34 Weber downdraft carburetor. This needed an adapter plate and the carburetor is NOT a direct bolt on as I had need told in the past. The carburetor did run all the time but it ran rough.
I ended up installing a Weber 32/36 with manual choke and it worked so I am keeping it now.

This is the adapter plate that was needed. This particular one only fit the 32/36.

Also, Autozone sells a gasket that fits the stock intake manifold. It's for a 1977-1979 Datsun 200sx.
The following gasket is the one that works on L series motors. The part number is G31154: