Rear Air Shocks to Coil Spring Conversion kit For BMW X5 E53 2000-2006 Rear Struts Shocks 19770818Features 1. Twin Tube structure allows sufficient stroke within the shock absorber. 2. High Tensile performance spring STRESS TESTED OVER 600,000 times while the spring distortion is less than 0. 04%. Plus the special surface treatment improves durability and performance. 3. Most pieces in our coil over systems, including mounts, collars, and spring perches, are designed from 6061 T6 Billet Aluminum resulting in lightweight, durable, and rust