When I gutted my 56 Flying Cloud, I generally was good about marking parts, but this one ended up in a bag with no identification:
The outer diameter is about 8 5/8", and the inner diameter is 5 1/2". The shadowing in the image shows that the inner circle is at a different elevation (maybe 1/2") from the outer circle.
My coach had a kitchen exhaust fan, but the pictured part does not seem to me to be part of that assembly (even though it is close in size to the exhaust fan opening in the sidewall).
Can anyone identify this part?