The 3" x 3" x 3" diameter galvanized furnace pipe straight tee is used for the gas heating, ventilation and air conditioning only. Not for use with solid fuel appliances. It is designed to connect pipes of the same diameter, but a reducer/increaser may be used to modify multiple pipe size connections if required (sold separately). This duct tee is made from 30-gauge galvanized steel for rust resistance and long-lasting durability.