Shorty design for power gain from idle to mid-range RPM. Gains 10HP and 10 lb-ft torque. Mitered merge collectors to maximize exhaust velocity and scavenging. Fully mandrel bent tubes made of 16-gauge, 409 stainless steel. Head flanges laser-cut from 3/8-inch thick steel plates. Flanges flattened by hydraulic press for precise and leak-free seal. Flanges chrome plated for corrosion resistance. All joints TIG welded for resistance against cracking and wearin. Shorty / Short Tube. 3/8 inches (9.5mm). 16 gauge (1.5mm). For track/off-road use only. No instructions provided; professional install recommended. Note: The items you received are shown in the figure. If you have any questions later, please contact the after-sales staff in time.