This gearmotor is a powerful brushed DC motor with 30:1 metal gearbox intended for operation at 12 V. These units have a 0.61″-long, 6 mm-diameter D-shaped output shaft.
Key specs at 12 V: 350 RPM and 300 mA free-run, 110 oz-in (8 kg-cm) and 5 A stall.