999-POLOLU 10:1 Micro Metal Gearmotor HP 6V
This gearmotor is a miniature high-power, 6 V brushed DC motor with a 9.96:1 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.
Key specs at 6 V: 3000 RPM and 120 mA with no load, 4 oz-in (0.3 kg-cm) and 1.6 A at stall.