Definition of Allen bolt
: 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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Origin and Etymology of allen bolt
Allen Manufacturing Co., Hartford, Connecticut
First Known Use: 1972
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