Revshift polyurethane differential bushings completely replace the oem rubber bushings on the E46 M3 and Z4M. These bushings stiffen the differential improving the vehicles handling capabilities. Will not wear out like oem bushings Properly dampens the differential Includes new class 10.9 bolts Revshift bushing lube included Improves handing Lifetime warranty Sold as a set Hardness80A black: Slightly stiffer and stronger than OEM rubber. No additional NVH. Great choice as an upgraded stock replacement (OEM+).95A green: Significantly stiffer and stronger than OEM rubber. Minor increase in NVH. Excellent for enthusiastically driven street cars and track cars.70D white: Drastically stiffer and stronger than OEM rubber. Moderate increase in NVH. Most commonly used on dedicated track cars.(NVH = noise, vibration, harmonics) Learn more about choosing polyurethane here: https://revshift.com/pages/polyurethane Please specify the hardness.