2011-14 Mustang GT headers with 1-7/8" primary tubes, 3" X-Pipe and 3" dia catted lead pipes that mate to the factory connection point. Tig welded 304 SS headers with 3/8" thick flanges and 3" dia slip fit collectors with merge spikes. This system replaces the factory manifolds, catalytic converters and H-Pipe with a superior performing lifetime guaranteed bolt-on system. 2011-14 Mustang GT headers with 1-7/8" primary tubes, 3" X-Pipe and catted lead pipes that mate to the factory connection point. Tig welded 304 SS headers with 3/8" thick flanges. This system replaces factory manifolds, cats and H-Pipe. 2011 thru 2014 Ford Mustang GT 5.0L