Check the listing for details. 5 1/2" Face 4" Back BEIGE Round Rotaire Grille Damper Heat AC Register Vent RV. Condition: New. Listed at 5.25 USD. 5 1/2" Face 4" Back DURA BEIGE Round Rotaire Grille Damper Heat AC Outlet Register Vent 3840RDB RV Trailer *Unique worm-drive damper (A worm drive is a gear arrangement in which a worm(which is a gear in the form of a screw) meshes with a worm gear (which is similar in appearance to a spur gear). The two elements are also called the worm screw and wormwheel.*Center knob opens and closes the vent wings. In fully open position the vent wings are completely retracted allowing 100% unrestricted air flow. *360 rotation *Easy installation and long term durability. *Accepts 4" flex duct. See tape measure pictures.Approximate size:Grille face diameter 5 1/2" Back diameter 4"Side: 2"Please let me know if you have any questions.Thank you,Babette