The Bolt Saver Bushing kit is for the rear differential bushing on the BMW X3M and X4M’s. The Bushing supports the mount bolt in 3 modes:
 
1. The aluminum insert removes the slop built into the oem insert removing the “running start” the differential had at bending or breaking the bolt. 
 
2. The Bolt Saver Bushing removes the distance from the differential mount flange to the rubber in the oem bushing. This removes the leverage the force had to bend the bolt and transfers the bending moment force closer to the mount location converting it into more of a shear force. 
 
3. The Bolt Saver resists the movement of the mount bolt in both compression AND Tension.  It resists in compression by the very hard and strong 75D shore hardness polymer material and it resists in tension by the dual carbon fiber rings inside of the polymer to reinforce it and limit give.