Pololu 12V 25:1 20D Metal Gearmotor (Long-life Carbon Brush)These small brushed Pololu 20D DC gearmotors can deliver a lot of power for their size. This version has a 12V brushed DC motor with long life carbon brushes combined with a 25: 1 metal spur gearbox. The gearmotor is cylindrical with a diameter of 20mm, and the D shaped output shaft is 4mm in diameter and extends 18mm from the faceplate of the gearbox. In general, these kinds of motors can run at voltages above and below their nominal voltages; lower