6V-12V DC Gear Motor uses a brushed DC motor with extra strong magnets and a 99:1 metal gearbox to deliver a lot of power in a relatively small package. These units have a 0.315” long, 4 mm diameter D-shaped output shaft. These motors are intended for use at 6 V. In general, these kinds of motors can run at voltages above and below this nominal voltage, so they should comfortably operate in the 3 – 9 V range, though they can begin rotating at voltages as low as 1 V. Higher voltages could start negatively affecting the life of the motor.