Header Type: Shorty / Short Tube. Primary Diameter: 1-5/8 in. Collector Diameter: 2-1/2 in. Head Flange Thickness:3/8 in. Pipe Thickness: 16 gauge (1.5mm). Material: 409 Stainless Steel. Horse Power Gain: +7.87 hp, Torque Gain: +12.03 lbs. Excellent quality and durability to improve vehicle performance. Shorty design for power gain from idle to mid-range RPM. Fully mandrel bent tubes made of high quality 16-gauge 409 stainless steel. Head flanges laser-cut from high quality 3/8-inch thick steel plates. All joints are golden color TIG brass style welded to prevent cracking and wear. The flange is flattened by a hydraulic press for precise and leak free sealing. Flanges chrome plated for corrosion resistance. Mandrel bent pipes to maintain free flow.