Z-Flex Z-Vent 3" Wall Thimble Stainless Steel Venting (2SVSWTF03) 3" Wall Thimble Stainless Steel Venting Wall thimble is used for horizontal exhaust venting through the outside wall Wall Thimble is 10" x 10" and has an adjustable width from 4" to 7" Rated AL29-4C and is approved for Category I (vertical only), II, III & IV applications Contains a built-in, fail-safe gasket and locking band connection