Vent connectors shall be constructed of metal. The minimum nominal thickness of the connector shall be 0.019 inch (0.5 mm) (No. 28 Gauge) for galvanized steel, 0.022 inch (0.6 mm) (No. 26 B&S Gauge) for copper and 0.020 inch (0.5 mm) (No. 24 B&S Gauge) for aluminum.