Pololu 5.1:1 Sub-Micro Plastic Planetary Gearmotor 6Dx14L mm

This tiny, cylindrical gearmotor consists of a coreless brushed DC motor and a 5.1:1 plastic planetary gearbox. The entire assembly has a diameter of just 6 mm (0.24″) and an extremely light weight of 1.2 g (0.042 oz), making it a great actuator for miniature robots and very small mechanisms. Key specs at 6 V: 13,000 RPM and 45 mA free-run, 0.3 oz-in (0.02 kg-cm) and 400 mA stall.