What is this?

[glatt]

Looks like a door would hang off of those hinge tabs on the left there. That means the thing is in its correct orientation, or is upside down. I think it's in its correct orientation, and a stove pipe type piece fits in the round lip. I have no idea what those notches are inside the circle. I'd guess some sort of notches to hold a damper in place at different settings.

I really am grasping here though. No idea.