Chevy 235 Intake Question

On my stock intake, and on the Fenton dual I am waiting to arrive, they both have a hole on the drivers side...maybe 1/2" NPT???. Anyways, it's plugged on the stock, and on the Fenton it looks like I need to plug it. What is this for? Can I mount a vacuum gauge in this hole? Thanks.

 

Vacumm source for wipers or whatever. Yes for gauge.

 

how much vacumm there?enough to run a brake booster?