Clockmakers (horologists) have their own jargon which we will stick to, as this is the terminology you will come across if you seek help and guidance elsewhere.

The spindle on which a gear is mounted is known as an arbor.

At each end of an arbor is generally a thinner section. This is known as a pivot, which engages in a pivot hole to form a bearing.

A small gear is known as a pinion.

A larger gear is known as a wheel. A wheel frequently engages with a pinion to form a reduction gear. Several such together form a gear train, transmitting the power of the spring to the escapement and the hands.

A wheel and a pinion are always mounted on parallel arbors, however, a contrate wheel (like a crown) can engage with a pinion on an arbor at right angles.