Micro annular gear pumps are miniaturized rotary positive displacement pumps. They are based on a so-called micro annular gear principle with an externally toothed internal rotor and an internally toothed external rotor. The internal rotor has one tooth less than the external rotor, with tooth ratios of 6/7 and 10/11. The manufacturing tolerances of the rotors are in the range of few micrometers.