hole in the back passenger side of the intake?

I have a 96 dodge ram 1500, it has the 5.9 v8, I just changed the intake manifold gaskets and noticed there is a hole in the back passenger side of the intake, it looks like a spot for a fitting but I never had to remove anything from that area to take the manifold off of the engine, my question is, what is that hole used for and is it ok to leave it open, also its a pretty big threaded hole. Any info would be greatly appreciated thanks.