Under dash ductwork 70 gs

I was working under my dash and had to remove the ductworks. Here is a picture of the center duct tube. Notice the small round hole mid ships. Is this hole stock and what is it used for?

thanks
Rick

 

Original......I've always thought it was a drain hole for condensation, etc.

 

That's a condensate drain... I remember my dads mid sixties big Buicks with chrome vents that would frost up; and the drivers side had a crotch cooler vent as well. I think my mom liked that one even better LOL... Bill in TR