This DuraVent chimney flue pipe is used in Category 1 gas appliances. (Do not use in wood burning ovens.) It measures 24" length with either a 5" or 6" diameter, and features twist-lock design for safe and easy connection / disconnection without mechanical fasteners. No locking bands are required. Features .012" aluminum inner and .018" galvanized outer. Outside dimensions 5/8" larger than inside dimensions. Limited lifetime warranty. Shipping is FREE in the contiguous US.