50:1 Micro Metal Gearmotor MP 6V with Extended Motor ShaftPololu
This gearmotor is a miniature medium-power, 6 V brushed DC motor with a 51.45:1 metal gearbox. It has a cross section of 10 × 12 mm, and the D-shaped gearbox output shaft is 9 mm long and 3 mm in diameter. This version also has a 4.5 × 1 mm extended motor shaft.
Key specs at 6V: 420 RPM and 40 mA with no load, 12 oz-in (0.9 kg-cm) and 0.7 A at stall.