The DuraPlus 8 in. Diameter Stainless-Steel Wall Thimble adjusts from a minimum of 4-1/4 in. to a maximum of 7-1/4 in. wall thickness, and fits between standard wall studs. To accommodate thicker walls, the telescoping thimble can be extended up to 16 in. with a field-fabricated extension installed. Its interior trim ring is painted black to help keep it insulated. This wall thimble must be installed with DuraPlus chimney pipe horizontally through the wall and extend a minimum of 2 in. into the room beyond the interior wall to function properly.