Product Description 3" inch, 3RV-UAF, Universal Female Adapter. Designed for round type B gas vent. Allows Metalbestos B-vent connectors to be used in conjunction with other brands of existing vent. Used to adapt to Metalbestos pipe toward appliance. Adjustable flange fits any wall. Permanent stainless steel seat. From the Manufacturer 3" inch, 3RV-UAF, Universal Female Adapter. Designed for round type B gas vent. Allows Metalbestos B-vent connectors to be used in conjunction with other brands of existing vent. Used to adapt to Metalbestos pipe toward appliance. Adjustable flange fits any wall. Permanent stainless steel seat.