Brand New 5 in. D X 7 in. D Galvanized Steel Stove Pipe Increaser The 5" Galvanized Steel Increaser is used to connect 5 inch diameter round pipe to 7 inch diameter round pipe. Sturdy, 26 gauge construction designed for optimal heat efficiency and long-term use. Crimped on one end to easily fit into pipe or fitting of the same diameter.r. Used to increase diameter of flue pipe perimeter when making connections Larger end is crimped for easy connection with same-diameter pipe or fitting opening For all heating, air conditioning and venting where rigid pipe is required 26-gauge cold-rolled steel construction for durability and lasting performance