A great mini gearmotor, at a decent price. The GM12a has a brass front faceplate, not steel.
Here are the performance measurements:
Running at 3V:
Free running speed: 85rpm
Free running Current: 18mA
Stall Torque: 15.6 in*oz
Stall Current: 290mA
Running at 6V:
Free running speed: 169rpm
Free running Current: 32mA
Stall Torque: 27.2 in*oz
Stall Current: 456mA
Dimensions: 30.4 x 12.0 x 10.1mm
Shaft length: 9.3mm
Shaft diameter: 3mm
Centered 3mm output shaft
Weight: 9.3g
Ratio: 100:1
Starts at 0.43V @ 14mA
Check the other documentation for a measurements data sheet.
0-GM12a
Measurements 
Solidworks Model