Airkit LLC eyeball air vent R3275-2.5 3" round vent mounts in 2-3/4 hole . They have a 2-1/2 inch SCAT hose adapter and a 1.87 air opening. Black Anodize aluminum construction. Single hole mounting just insert vent and thread hose adapter on the back. They are backed by a 1 year manufacture warranty.  

More are available if needed message me for lead time

2 inch hose adapter is also available