Fastener Guides

A castle nut is a slotted hex nut designed to lock with a cotter pin through a drilled bolt or spindle. On fleet steering, suspension, and wheel ends, that positive lock beats a nylon lock nut you cannot inspect at a glance. Here is how to choose, install, and stock castle nuts before winter vibration and salt find the weak joint.

Most cotter pin failures start with a pin that already did one job. Here is how fleet and equipment shops pick diameter, length, and style, and why critical retention almost always means a fresh pin.