Kooks Custom Headers PN6920 (headers) and cat pipes PN1002741 are constructed from 304 stainless steel. The headers have a 3/8-inch thick flange, 18-gauge 17⁄8-inch-diameter tubes, and flow into a 3-inch-diameter collector. Three-inch stainless steel cat pipes link the Kooks headers to the factory catalytic converters. To eliminate header flange leaks, Kooks uses Percy's High Performance 3/8-inch thick carbon gaskets. A pair of Kooks O2 sensors replace the factory sensors.