I need your help with my vacuum tap (and my manifold studs, too).

The factory port in the intake is 3/8npt (national pipe thread) and is tapered. The fitting you have is a tube thread and is straight threads like a bolt. The fitting you need will have the same size hose barb as the new fitting, but will have the correct 3/8 NPT threads for the manifold. Since the threads are tapered, you do not tighten it all the way down, or you will break the manifold. They only tighten in a few threads. Make sure to seal the threads with something too.