B-vents are make to attach and adapt to a wide variety of different size chimney pipe systems. A B-vent adapter is designed to connect the primary chimney liner system to other B- vent type pipes that go to appliances. The B-vent adapt is constructed from aluminum, 3003 alloy. The sizes include three inch, four inch, five inch, five and one-half inch and six inch adapters. These adapters are ideal when you have to install components from different brand of liner systems.