‘67 Barracuda vacuum gauge connection

Redfish - Thank you - that makes sense now. I remember the intake manifold fitting that was on the car had a vacuum connection that probably was 1/8. I probably still have that fitting, which may or may not have been original to the car, but worked with the original hose.

Vacuum hoses for 1/8 fittings seem to be listed either as 1/8 (fitting size) or 7/64 (hose ID). Gates lists by hose ID.