Ford, Big Block Ford Down and Forward Turbo Headers. All tubes are CNC mandrel bent for optimal flow. Made from 304 stainless steel for maximum corrosion resistance. Starting with a CNC cut 3/8″ thick flanges into 2″ diameter primaries, Flow into 3-1/2″ slip-fit collectors. Headers are fully TIG welded and back purged. Header flanges must be specified by customer. Recommended header flange is HFBBF1-200. Mill finish, These, are TIG welded for strength and durability. These kits come with a lifetime warranty and proudly made in the USA.