Over time the original plates in your diff lose friction material which can cause them to wear down to metal on metal. The limited slip differential plays a key part in your vehicles handling setup so when it's time to rebuild your LSD diff, then you'll need replacement springs & plates, look no further than the genuine MFactory parts to restore optimum potential to your LSD. For the 12 piece set you will receive 6 outer plates, 6 inner plates and 12 springs. For the 20 piece set you will receive 10 outer plates, 10 inner plates and 20 springs.