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The Encyclopedia of Horology

Glossary · Mechanism

Bumper (wig-wag) winding

An early automatic-winding system in which a semicircular oscillating weight winds the mainspring on both swings via a spring buffer.

Explanation

Preceding the full 360-degree rotor, bumper systems used springs to reverse the weight's swing once it reached the case edge; largely superseded after the Second World War by full-rotor designs.