The Clutch Masters 07-05 Audi S4 4.2L B7 850 Series Street and Race Twin Disc with Steel Flywheel is a high performance clutch system designed for street and race applications. It features a lightweight steel flywheel and a twin disc design that provides superior torque capacity and smooth engagement. The 850 series is designed for high performance applications, offering increased holding power and durability. It is ideal for those looking for a reliable and powerful clutch system for their Audi S4.