What is this manifold hole for?

[OzCuda]

Edelbrock 383 Torker inlet manifold, rear below carby.  Is this for the brake booster?  Anyone know the size and thread?  thanks, Mark.

[Chryco Psycho]

if you plan to use a pcv valve i use this port for pcv as it will more evenly distribute to all ports , for brakes i use a port on 1 runner or off the carb