Allen bolt
noun
Al·len bolt
| \ ˈa-lən-
\
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Definition of Allen bolt
hardware
: a bolt with a hexagonal socket in its head that is designed to be used with an Allen wrench
The Allen bolt is integral to the crank and remains in it when the crank is removed from the spindle.— Eugene A. Sloane, Sloane’s New Bicycle Maintenance Manual, 1981
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