M G Duravent 8DT-WT 8 Inch Duratech Wall Thimble Galvanized Steel Painted Black Finishing Collar Needed Not Included The 8in DuraTech Wall Thimble is used in through-the-wall applications the wall thimble adjusts a minimum of 4in to a maximum of 10in and fits between standard wall studs. To accommodate thicker walls the telescoping pieces can be separated and a field fabricated extension may be installed. The interior trim ring is painted black. The wall thimble must be installed with DuraTech Chimney pipe horizontally through the wall sufficient in length to extend from the tee 6-inches into the room from the interior wall.