The Bilstein B4 01-06 BMW M3 Base Rear Twintube Shock Absorber is a performance-oriented suspension upgrade designed to provide improved handling and stability for BMW M3 vehicles from 2001-2006. This shock absorber features a twintube design that is optimized for superior damping characteristics, and its monotube design provides superior ride comfort. The Bilstein B4 shock absorber is constructed from high-quality materials and is designed to provide a long service life. It is also corrosion-resistant and comes with a limited lifetime warranty.