In order to reduce or divide the number of rotations in a gear train it is necessary to have two gears per axis.

The smaller of the two gears is called a pinion and is made of hardened steel. It has between 6 and 14 teeth. The larger gear is called a wheel and is usually made of brass except for the escape-wheel which is also made of steel.

These gears can have different qualities. The highest quality will have the wings polished with diamondine that will be put on a worm, generally made of pear wood. The more the teeth are polished, the less force is needed and the finer and longer the spring can be. Thus the power reserve can be longer.

Also the very high end pinions have a pitting in the face and polished faces. The wheels are riveted to the pinions.