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It is difficult in practice to use things like this as step up gear boxes. Even a tiny amount of friction at the output would require absurd torque to overcome. The gears are more or less self locking at some point as increasing the torque increases the normal force between the gears and the required torque is always more than you can apply.

Think of a nut and all thread. You can spin the nut up and down the thread with a huge mechanical advantage. However it is difficult to push on a nut to rotate the threaded rod unless the thread is course and very low friction