Balance wheel

1. (Horology) A wheel which imparts regularity to the movements of any engine or machine; a fly wheel.
1. A wheel which regulates the beats or pulses of a watch or chronometer, answering to the pendulum of a clock; -- often called simply a balance.
2. A ratchet-shaped scape wheel, which in some watches is acted upon by the axis of the balance wheel proper (in those watches called a balance).