In a reduction gear train, the intermediate gears are clusters. The driven gear has a pinion attached that drives the next gear. The gear might have 50 teeth, and the pinion as little as 10 teeth. If the pinion drives a next gear of 60 teeth, the stage gear reduction ratio is 6:1.
Frequently the pinion is longer than the mating gear because it requires overlap on both sides, and it requires a longer face width to accommodate the higher stresses that pinions experience.
As you progress in the gear train, the pitch generally becomes coarser. There are higher loads and stresses because the cluster torque keeps going up stage by stage. Also, the face widths tend to increase with every stage for the same reason.