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The Encyclopedia of Horology

Component record · Keyless work

Clutch Wheel (Castle Wheel)

Verified

A splined wheel, also called the castle wheel, that slides along the winding stem's square section and can be shifted between winding and hand-setting positions.

What it does

Engages the winding pinion train to wind the mainspring in one crown position, and disengages to instead drive the setting train when the crown is pulled out for hand-setting.

How it works

The clutch wheel's internal splines mate with a squared or splined section of the stem, allowing it to be driven rotationally by the stem while sliding axially along it.

Pulling the crown out moves the stem, and with it the clutch wheel, along its axis via the yoke; this shifts the clutch wheel out of mesh with the winding pinion and into mesh with the setting wheel(s) that ultimately turn the hands.

Pushing the crown back in returns the clutch wheel to the winding position, re-engaging the winding pinion and disengaging the setting train.

Evolution

Keyless works with a sliding clutch wheel superseded separate winding keys through the second half of the 19th century and became close to universal by the early 20th century.

Known variations

  • Sliding-pinion (clutch wheel) systems
  • Rocking-bar keyless works, an alternative keyless mechanism using a pivoting bar rather than a sliding clutch

Identification for collectors

  • Visible under the dial as a splined wheel riding on the stem, shifting position when the crown is pulled or pushed

Common failure modes

  • Worn splines causing the clutch wheel to slip on the stem
  • Yoke or setting-lever wear preventing clean engagement in either position

Photographs

Universal Genève 138SS keyless works with the sliding pinion on the stem — source reports a missing tooth; in-situ context, not an isolated pristine clutch wheel
Universal Genève 138SS keyless works with the sliding pinion on the stem — source reports a missing tooth; in-situ context, not an isolated pristine clutch wheel — Watch Guy workshop photo library; individual photographer not separately stated, Copyright workshop photograph — rights pending; permission not established; reduced-size JPEG copy. Watch Guy — photo P8041540, source-captioned sliding-pinion fault

Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.

Sources & references

  1. de Carle, D., Practical Watch Repairing

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