A rotor cap assembly has been conceived using multiple wedge-shaped rotor cap segments, in which the cap segments are disposed on a cap segment retainer and in which the cap segment retainer pilots the multiple rotor cap segments at a diameter intermediate the cap segments' outer diameter and the cap segments' middle diameter. By piloting multiple rotor cap segments with retaining means on the cap segment retainer and positioning means on the multiple cap segments, the rotor cap segments and cap segment retainer assembly may be fixed to a plate holder or directly to a rotor disc of a refiner without substantially altering either the plate holder or the rotor disc.