Allen bolt

noun

Al·​len bolt ˈa-lən- 

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

Word History

Etymology

Allen Manufacturing Co., Hartford, Connecticut

First Known Use

1972, in the meaning defined above

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