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The Encyclopedia of Horology

Component record · Regulation

Curb Pins

Partially verified

The pair of pins on the index between which the hairspring passes.

What it does

Set the spring's effective length, and so the rate.

How it works

Moving the index changes how much spring lies outside the pins, altering rate.

Pin spacing matters: too wide and rate varies with amplitude, too tight and the spring binds.

Evolution

Refined by swan-neck and micrometric regulators giving finer control.

Known variations

  • Plain curb pins
  • Boot-and-pin arrangements

Identification for collectors

  • Visible under a loupe where the hairspring passes the index.

Common failure modes

  • Unequal spacing causing isochronism errors
  • Bent pins trapping the spring

Diagram

top plate or bridgespillar platebalance and cockwheel train between the plates
Schematic: plate and bridge layout. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. de Carle, D., Practical Watch Repairing
  2. de Carle, D., Watch and Clock Encyclopedia
  3. Daniels, G., Watchmaking

Where sources disagree, the disagreement is stated rather than resolved silently.