balance wheel(n = noun.artifact) balance - a wheel that regulates the rate of movement in a machine; especially a wheel oscillating against the hairspring of a timepiece to regulate its beat;
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. [1913 Webster]
A wheel which imparts regularity to the movements of any engine or machine; a fly wheel. [1913 Webster]