This 2.5" diameter optional mid section is designed to work ONLY with BORLAÂ Axle-Back systems 11981 & 11981BC. Installation REQUIRES cutting the mid section of the stock exhaust behind the catalytic converters and welding the inlet pipes in 60738 to rear of catalytic converters. It features a Merge X-Pipe for increased performance and improved sound. The mid section will increase the overall sound volume while maintaining the S-Type tone of 11981 & 11981BC. Combining the 60738 mid section with Axle-Back systems 11981 or 11981BC will create a Cat-Backâ„¢ system. Each system is built from premium T-304 stainless steel superior to T-400 series knockoffs (such as 409) to give you the absolute best in performance and durability. Ultra-smooth mandrel bends ensure maximum flow & power and precision computer numerical control (CNC) manufacturing ensures an accurate fit. Best of all BORLAÂ stands behind every system with a Million-Mile Warranty. Just what you'd expect from the world's most experienced (and most winning) exhaust brand.