Selkirk 4-in x 1-ft Galvanized Steel/Aluminum Pipe for Natural Gas, UL441 Listed, 400F Max Temp, 0 PSI Max PressureDesignated for use on approved gas appliances, the 4 in. x 12 in. round type B adjustable gas vent pipe is ideal for residential, light commercial and industrial applications. The exclusive lock tab feature offers versatility to installation. Rugged construction, assured safety and fully tested and listed per UL 441. Size refers to the inside diameter of the pipe or fitting The outside diameter is approximately 1 2 inch larger Outer material is 28 gal