Selkirk Metalbestos 3RV-18 3-Inch X 18-Inch RV Gas Vent Round Pipe Designed for use on approved gas appliances in residential and light industrial application Involves incorporating a LockTab in the female end of each gas vent section a accessories The incorporation of a LockTab feature simply improves our lock system by adding flexibility and meeting market needs Gives installer the option of engaging the LockTab instead of using sheet meal screws Round pipe design