A pump or motor having a three-lobed rotor capable of being used within a hypocycloidal two-lobed stator that is designed primarily for use with a one-lobed rotor. The three-lobed rotor design allows for interchangeability with the two-lobed stator to provide for varying fluid displacements to meet particular demands. A specific application allows for the combination of both the three-lobed rotor along with a one-lobed rotor within the same two-lobed stator, thereby improving the efficiency of the pump or motor.