overcoil

[ oh-ver-koil ]
/ ˈoʊ vərˌkɔɪl /

noun Horology.

a fixed end of a spiral hairspring, consisting of an upwardly and inwardly bent continuation of the outermost coil of the spring: used to offset the asymmetry of the common spiral spring when tight, which impairs isochronism.
a hairspring having such a fixed end.

Origin of overcoil

First recorded in 1880–85; over- + coil1

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