Examples from the Web for hairspring
The gradual weakening or loss of elastic force of the hairspring is also a factor to be considered.
The Curb Pins sometimes produce the ferric oxide mentioned by their action on the hairspring.Friction, Lubrication and the Lubricants in Horology|William T. Lewis
The hairspring should be removed and the pivots known to be straight and polished before testing.
When rust begins its attack upon any point of a hairspring there will be a constant loss in time until its advance is stopped.
Thus the balance receives the power to keep it in motion, swinging it as far as the hairspring allows.Time Telling through the Ages|Harry Chase Brearley