3″ diameter into 2.25″ Y-pipe. Adding this Mid-Pipe/Y-Pipe to an Axle-Back system will give you all the elements of a Cat-Back™ system. These Mid Pipes are NOT intended for use with OE factory mufflers. Built from premium T-304 stainless steel, superior to T-400 series (such as 409), to give you the absolute best in performance and durability. Ultra-smooth mandrel bends ensure maximum flow & power, and precision computer-controlled CNC manufacturing ensures an accurate fit.