6" gated exhaust port

I needed a small 6" exhaust port for a 6" inline duct fan to vent laser fumes out of the house. As I didn't want to just hang it out an open window, I decided I'd drill a 6" hole in the back door of the shop, and vent it that way. This has 4 #10 machine bolt holes to attach it to a wall/door/piece of wood/whatever. It has a 6" coupling to attach a 6" duct/dust hose to, and a blast gate to close things off so you can keep out critters/bugs when not in use.

It's not a proper blast gate in tha