Inner Diameter: 5 x 8 . Required for Installations that Pass Through an Attic ...Inner Diameter: 5 x 8 . Required for Installations that Pass Through an Attic to Prevent Insulation and Debris from Accumulating near Vent. Length: Adjusts from 11 to 20 . Width: 9-316 . The DirectVent Pro 5 x 8 Inner Diameter Galvanized Attic...more