The Bilstein B4 Series 19-158839 is a premium twin-tube gas pressure shock absorber designed to restore your vehicle's original ride quality and handling. Specifically engineered for the rear axle of BMW Z3 models, it offers constant damping power under any load and high power reserves for maximum safety. This product is sold as a single unit. List of parts included: 1x Shock Absorber (Art: 19-158839), 1x Mounting Nut. Features: OE quality, gas pressure technology, and easy bolt-on installation.