SPG50 is 3.4W DC brushed motor with compact size, a low cost solution for projects such as medium size robot, omni drive robot, mechanism, etc. This model of SPG50 brushed motor comes with gear ratio of 20:1 and can operate up to 12 volts (tested 9V to 15V). Each motor is 6mm diameter D-shaft.
Note:Lower voltage might not have enough torque to drive the wheel or mechanism; higher voltage will provide higher torque and higher speed, but it will shorten the life of the motor.
For mounting, the depth of the thread of the motor is 3.2 mm. So, you need to use 3.2 mm length of M3 size screw (not included with the thickness of the bracket). Longer screw will damage the gear box. You may need to consider the thickness of the bracket or other mechanism that you need to attach to the motor for choosing the right length of screw.