Balance wheel : 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.

Balance wheel : 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).

Balance wheel : A wheel which imparts regularity to the movements of any engine or machine; a fly wheel.

Example:


Taxonomy
balance wheel, balance, balance wheels, balance spring, watches, wheel, clock, timekeepers, arms, 2007-06-15, New York, Milham, 1945, temperature compensation, beat, marine chronometers, TimeZone, weights.

Defination from the web:
balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring. ...