Mandrel bent tubes provide consistent tubing diameters for better exhaust pulse flow and improved performance 1-1/2 in. and 1-5/8 in. primary diameters available for increased exhaust flow and improved throttle response Heavy duty 16-gauge 409 Stainless Steel used for strength and durability 10 in. long, 2.5 in. collector improves exhaust flow 3/8 in. thick header flange for a leak-free seal and maximum strength Available for both round and D-port exhaust ports Header gaskets included