4" Type B Gas Vent Male Adaptor 4GVAM This male adaptor is used to connect existing DuraVent Type B Gas Vent to a listed Type B Gas Vent system manufactured by other companies. Male adaptor can also be used to attach to DuraFlex AL. 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