Castle Nut

A castle nut is a slotted hex nut designed to be used with a drilled bolt or shaft and a cotter pin. After tightening to the specified preload, the slots are aligned with the cross-hole in the fastener, and a cotter pin is inserted to provide positive mechanical locking. This design prevents nut rotation under vibration or dynamic loads, making castle nuts suitable for safety-critical and rotating applications where loosening must be mechanically prevented.