Hairspring

The hairspring (German Spiralfeder or Unruhspirale) is the spiral spring attached to the balance wheel. It provides the restoring force that returns the balance to rest after each impulse. Together with the balance it forms the oscillator — and is, alongside the balance wheel, the most critical timekeeping component in a mechanical movement.

How the hairspring works

When the balance rotates in one direction it stretches the hairspring; the stored tension pulls the balance back. As the balance swings past rest in the other direction it compresses the spring; tension again pulls it back. The cycle repeats, regulated by the spring's specific stiffness and the balance's mass distribution.

The natural frequency of the balance-hairspring system determines the beat rate. Changing either the spring's effective length or the balance's mass distribution shifts the rate — that is the point at which regulation acts.

Hairspring materials

Material is where most modern hairspring innovation has happened:

• Steel (traditional, pre-1930s). Susceptible to magnetisation; temperature-sensitive.
• Nivarox and Glucydur alloys (mid-20th century onwards). Improved temperature stability and reduced magnetic susceptibility. Standard for mid-tier modern movements.
• Parachrom blue (Rolex proprietary, introduced 2000). Niobium-zirconium alloy. Paramagnetic, significantly more shock-resistant, with a visible blue tint.
• Silicon (Patek Philippe Spiromax 2005, Omega Si14 from 2008). Entirely non-magnetic, lighter, geometrically stable. Some collectors prefer traditional metal hairsprings as a heritage feature.
• Silinvar (Patek Philippe variant). Silicon-based with specific geometry for thermal compensation.

Silicon and Parachrom-style alloys are what enabled modern anti-magnetic certification — Omega Master Chronometer ratings to 15,000 gauss rely on these materials.

Hairspring geometry

Beyond material, geometry matters:

• Flat hairspring. Traditional flat coil, simple to manufacture, slightly position-sensitive.
• Breguet overcoil. A raised section of the outermost coil that improves positional consistency. Common in high-end movements (A. Lange & Söhne, Patek Philippe, some Vacheron).
• Phillips terminal curve. A specific mathematical terminal-coil geometry that minimises positional error.

Why the hairspring matters

At our atelier in Munich, hairspring problems appear as a severely off-rate movement that does not respond to standard regulation or demagnetisation. A typical finding is a bent or distorted spring after a shock — the coils no longer space evenly, the centre of mass shifts, and positional consistency and beat error deteriorate. A damaged hairspring is one of the most delicate watchmaking repairs and is usually a workshop case — for certain premium calibres, only the manufacturer itself.