A centrifugal pump with a cutter mechanism consisting of a toothed cutter rotor, integral with the impeller wear ring, affixed to the impeller and a toothed cutter stator affixed to the casing, separately from the casing wear ring. A cutter mechanism consisting of a stator and rotor set such that they may be installed on the centrifugal pump impeller and casing as original equipment or as a retrofit. A cutter mechanism such that when installed in a centrifugal pump they prevent stringy materials, garbage and other agglomerated soft wastewater solids from partially restricting or totally blocking the inlet to the pump impeller. A cutter mechanism such that when it prevents solids from restricting or blocking the impeller inlet, it does so without significant decrease of flow throughput or significant increase in absorbed hydraulic horsepower.