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The Encyclopedia of Horology

Glossary · Mechanism

Mainspring bridle (slipping spring)

A friction sleeve within a going barrel that lets a fully wound mainspring slip rather than stall.

Explanation

The bridle grips the barrel wall by friction until the spring's tension exceeds a set threshold, at which point it slips, protecting the winding mechanism and giving a more even torque curve near full wind, common in going-barrel automatic movements.