2203-POLOLU 50:1 Micro Metal Gearmotor LP 6V with Extended Motor Shaft
This gearmotor is a miniature low-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 6 V: 250 RPM and 40 mA with no load, 7 oz-in (0.5 kg-cm) and 0.36 A at stall.