This 4 Inch - 6 Inch Pellet Chimney Adapter from the PelletVent Pro series is a Type L Biofuel Chimney Pipe component and consists of the duralock system for a tight seal. Use to transition between PelletVent Pro to existing chimney such as DuraTech, DuraPlus or DuraPlus HTC. Requires a DVL/DuraBlack Chimney Adapter to fasten into support box or wall thimble, for 6", use adapter 8674, for 8", use adapter 8874. Features: Type: Adapter. Type L Biofuel Chimney Pipe Component. Use to Transition Between PelletVent Pro to Existing Chimney. Specifications: Overall Dimensions: 7" (H). Size: 4"- 6".