Installer Series™ Aluminized Steel Cat-Back Exhaust System with Single Rear Exit by MBRP®. With 2.5" Turn Down Assembly. Exhaust System Type: Cat-Back. Exhaust Tubing Material: Aluminized Steel. Main Tubing Diameter: 2.5". Exhaust System Sound: Moderate. Made of 100% heavy gauge aluminized steel MBRP Installer Series is designed to provide the cost conscious consumer with the same high quality design and craftsmanship as our other systems, but at a value price. Installer Series is suitable for areas with moderate environmental conditions.