I just want to share a few photos of my kiln vent project.
The pin and its bushing were machined out of mild steel. The round foot - aluminum.
I didn't machine the circular top collar: I just found it in my scrap bin and used "as is" (the holes drilled in the collar do not interfere with its function, so I just left them alone).
I used the vent during several firings, then sandblasted the newly formed rust away and painted everything to finish the project. The pin was not painted. I blackened it to protect against rusting (it was heated, and used machine oil was rubbed into the surface). It looks like rust on the photos, but it's not. The inside of the bushing should be done the same way.
As you can see, magnets are used to regulate fresh air intake.
P.S. If I ever make one again, I'll use aluminum or stainless steel for everything (except the connection to the galvanized exhaust). Naturally, I'll have to make some kind of shutters instead of magnets then. This would require no painting and won't rust.