7" Type B Gas Vent Storm Collar 7GVSC 7" Type B Gas Vent Storm Collar is used to maintain a weather tight resistant seal between the pipe and the flashing. Diameter: 7" Maintains a weather-tight resistant seal Durable construction can withstand the elements .010†Double-wall aluminum flex inner wall (two-ply .005â€) .018†galvalume outer wall with twist-lock connections.