Gears torque limits

I was wondering how you would calculate the torque of what the gear is using because on the techical info on the gear kit it says torque limits
12-tooth 40 in.-lbs.
36-tooth 120 in.-lbs.
60-tooth 200 in.-lbs.
any help is appreciated

The stall torque on the motors is 6.5 pound-inches, which is the torque which the motor produces. From the gear ratios you can calculate the torque being applied to any gear. The only problem with this is that it would take an incredibly large torque to damage an unloaded driving gear. Is it possible that the torque limit is the maximum difference in torque applied to the driving and driven gear?

Another thing: the specification indicates that the square hole has a much lower torque limit than the gears, but whenever I damage gears, its the teeth that break. Does anyone know about this?