Skip to content
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

Bumper (wig-wag) winding is the early automatic system in which a semicircular weight swings through part of a circle and bounces off spring buffers, winding in one direction of swing. John Harwood's 1920s patents made it the first practical self-winding wristwatch. The bumping feel on the wrist identifies the type; full 360-degree rotors followed in the 1930s–40s.