Magnetic Gears have been proposed for motion transmission since years 80s of last century. Their main characteristic is the torque transfer between two coaxial permanent magnets rotors through the interaction with a set of ferromagnetic poles but without mechanical contact. From the kinematic point of view their working is similar to the one of epicyclic gearing or planetary gearing and they can transmit torque with a constant gear ratio determined by the number of permanent magnet pole pairs and of modulating iron poles. A test bench for measuring magnetic gear performance has been devised and realised. Magnetic gears have been equipped with sensors coils to monitor the magnetic flux inside the structure and to compare it with simulation predictions.