Selkirk RV 4" Aluminum Tee Cap is the solution for sealing off any unused openings in your gas vent pipe, especially when located at the bottom of a Tee junction. This cap both effectiveness and convenience, as it can be easily removed for system maintenance whe needed. The size refers to the inside diameter of the pipe or fitting, with the outside diameter of the RV being approximately 1/2" larger. Designed specifically for Type B gas vent systems, this aluminum Tee Cap ensures reliable performance and safety in your venting setup. Trust Selkirk for quality and durability in all your gas venting needs. Model Number: 104180