The SMI series of built-in rotor/stator units are used in the production of liquid-cooled electrospindles, both analog and digital type, with high specific power rating and rpm. They enable the tool to be inserted directly on the rotor built-in shaft. This solution permits torque transmission without play and losses due to frictions, thus reducing the overheating of the operating heads, which can reach a speed of 40,000 rpm The range of rotor/stator units is very wide with constant power range of 1:2 to 1:12, obtained through winding commutation, providing two speed ranges. The internal boring of the rotor permits the setting of the motor shaft, housing tool clamping and cooling devices.