Vacuum Threaded Fitting with Nipple

I have a '72 V12 S3 that has an open 3/8" port on the front RH intake manifold. I need to close this but cant find the threaded fitting. Checked with SNGB but they don’t show it in their catalog. This is an EX/EM car, but I am trying to eliminate leaks. This is a BIG one. There is a threaded fitting on the LH rear intake so I know they existed. I thought it may be a 3/8 NPT thread but it is not.
Bob W, Spokane WA area

can you post a pic of this - manifold position, are you able to access with a thread gauge, if reasonable easy access i do have a suggestion but will hold on that as i’m sure i’ll get negative response from some die hard posters

I had the same frustration of finding a threaded plug that would fit. I ended up using a non-threaded black plug made of a pliable synthetic material (can’t remember exactly what) with some silicon around the perimeter. It seemed to work okay, but has not been tested in service.

Is this the port of which you speak?

Thanks friend. SNGB offers a rubber plug, doesn’t seem correct for a threaded fitting. Appreciate your response.

Hello Tom,
I received a reply with a picture of the plug. Just waiting to find where he found it. Thanks for your reply.

1 Like

I think I found my plug at a well-stocked hardware store and ground it down a little to fit. And yes, Craig, that is the port we are speaking of - at least the one I was talking about.

Thank to ALL who helped me with vacuum problem. Today I found a proper fitting from a local hose supply company who carried BSPP.
If anyone in the future has this need ask for “blanking pug 3/8-19 bspp”. Make sure it is parallel thread bsp(p) and NOT bsp(t) which is tapered.
Bob W