8" Type B Gas Vent Storm Collar 8GVSC This storm collar is used to maintain a weather tight resistant seal between the pipe and the flashing. For Category 1 gas appliances 1" clearance to combustibles Easy-fit twist-lock design with no fitting hassles 0.012" aluminum inner 0.018" galvanized outer .010†Double-wall aluminum flex inner wall (two-ply .005â€) .018†galvalume outer wall with twist-lock connections.