993-POLOLU 30:1 Micro Metal Gearmotor LP 6V
This gearmotor is a miniature low-power, 6 V brushed DC motor with a 29.86:1 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: 440 RPM and 40 mA with no load, 4 oz-in (0.3 kg-cm) and 0.36 A at stall.
micro metal gearmotor dimension diagram