DuraTech Class A Finish Collar 5" to 8" DPO The Tee Support will provide The Tee Support will provide the necessary clearances that are required for the chimney pipe to combustible material The DuraVent Direct Vent Pro Co Axial to Co Linear Adapter Kit (Masonry Fireplace Adapter Kit) allows you to install a direct vent gas or propane fireplace inside a masonry fireplace The DuraTech Finish Collar is used to make the transition from the DuraTech Class A chimney pipe to single wall stove pipe for through the wall applications and when the chimney pipe is suspended with a roof support system The DuraTech Finish Collar simply twists into the male end of the DuraTech pipe and reduces down to a single wall pipe end