DuraBlack 7″ Oval-to-Round Adapter The DuraBlack 7″ Single Wall Stovepipe Oval to Round Adapter is a component that is used in a typical venting installation. The oval to round adapter connects to the oval flue outlet to the appliance which has a round outlet. This must be field ovalized. Features: Type: Adapter. Converts Oval to Round. Must be Field Ovalized. Adapter Type: Single Wall Stovepipe. UL Listed. Specifications: Overall Dimensions: 12″ (L). Inner Diameter: 7″.