The DuraTech 7 Class A Chimney Pipe Locking Band is optional. It is used for extra security at pipe, elbow, and tee joints.For class a chimney pipe UL ListedADA Compliant: No Collection: DuraTech Fuel Type: Coal, Gas, Oil, Wood Inner Diameter: 7 Material: Galvanized Steel Outer Diameter: 9 Pipe Class: Class A Pipe Shape: Round Style: Functional Weight: 10 Width: 9