6" DuraVent DuraLiner 13" X 18" Round Extend-A-Cap Kit 6DLR-KXC18 6" DuraLiner 13" X 18" Round Extend-A-Cap Kit is used to terminate DuraLiner at the top of the masonry chimney. Kit includes: Base Plate Support Clamp Storm Collar and Cap. Pipe not included. Diameter: 6" Dimensions: 13" x 18" Kit includes: Base Plate Support Clamp Storm Collar and Cap Pipe not included .016†304 stainless steel inner liner. Rigid relining pipe: double-walled with 304 stainless steel inner and galvalume outer. Factory insulated between inner and outer walls.