HP rotors are close tolerance machined with smooth turned pad faces. The additional mass of the HP series extends service life on heavier competition vehicles and other severe duty applications. HP rotors are close tolerance machined with smooth turned pad faces. The additional mass of the HP series extends service life on heavier competition vehicles and other severe duty applications. They are also the base model for every day use. Each rotor is precision machined to less than .001 in tolerance for overall flatness, parallelism, and radial run-out on long grain carbon iron castings. Long grain carbon iron is used for its superior thermal conductivity and stability properties that resist distortion and fatigue.