The balance wheel
The balance wheel is the clock-setting part of a no longer stationary wheel clock (e.g. a pocket watch). The name came about after 1675, when Christiaan Huygens introduced the pendulum and the spiral spring as a regulator in his patent.
Its predecessors were the Unrast with scales and the torsion spring that Peter Henlein used in his can clock in 1505.
Image: Chris Burk's Wikipedia
The foliot, which means 'trembling leaf'.
It consisted of a balance beam that was hung on a thread. Its oscillation duration is several seconds, while the spiral spring oscillates approx. 5 to 10 times per second.
In 1660 Robert Hooke used a straight steel spring as a suspension instead of a thread.
Graphic: Wikipedia Public Domain