Performance Friction 01/83 is one of the most popular race compounds in PFCs arsenal.  At the end of the stop, 01 compound has less torque scatter for improved modulation with excellent release and a flat torque curve. 01 compound is very easy on the discs with very low wear, on par with 83 compounds. The same can be said for the 11 compound.  Performance Friction 97/14 and 81 Compounds have a less aggressive pad torque-wise than 01/83 and 11 compounds, these are commonly used on the rear of race cars for better brake balance. Sold per Calipers worth.