The balance wheel, is conventionally (but with exceptions) a circular, moving wheel that oscillates on its balance staff / central axis.
The balance spring, on the majority (99.9%) of watches is the spiral shaped spring that causes the balance wheel to oscillates at a specific frequency.
The Breguet overcoil, is made from the last coil on a balance spring, that is raised and crosses several of the inner coils before being fixed to the 'stud'. It allows for the spring to breath concentrically.
The balance cock, when the balance wheel is held in place by a bridge held by one or two screws but from one side, the bridge is referred to as a 'cock'. When a balance or other component is held by a piece which traverses the wheel or piece and is screwed in place on both sides, the piece is referred to as a bridge. (Bridging the wheel).
The (balance spring) collet, the component that the balance spring is attached to which then is pushed onto the balance staff.
The (balance spring) stud, the component by which the balance spring is attached to the balance cock.
Helical, the form of a helix. Helical balance springs were traditionally used in marine chronometers.
The index, found on the balance cock, it is a component for adjusting a watch's rate by altering the effective length of the balance spring.
Inertia blocks/maslots, off set weights added to balance wheels for regulation.
Associated terms
Amplitude, the maximum angle by which a balance oscillates from its position of rest. According to the amount a watch is wound and the position of the watch (ie horizontal or vertical), the amplitude will vary between 180° and 315°.
Frequency, the number of oscillations per second, measured in Hertz. The balance oscillates at a given frequency. 21,600 vibrations/hour (3 Hz), 28,800 vibrations/hour (4 Hz) and 36,000 vibrations/hour (5 Hz).
Hertz, Unit of frequency (number of periods or cycles per second).
Terminal coil, the final coil on a balance spring modified in form to interact with the regulation system and/or stud.
Vibration "Movement of an oscillating body between two extreme positions.
The balance of a mechanical watch generally makes five vibrations per second, equivalent to 18,000 vibrations/hour (2.5 Hz). A more accurate mechanical watch makes 10 vibrations per second or 36,000 vibrations/hour (5Hz). A quartz crystal vibrating at 32,678 Hz is 32 kiloHertz (KHz).