What is typically used in conjunction with a castellated nut?

A castellated nut is designed with castellations or grooves on its top, allowing for a locking mechanism when secured properly. The typical practice involves using a split pin to maintain the nut in place. When the castellated nut is tightened to a specific torque on a shaft or bolt, the pin can be inserted through the nut's slot and a corresponding hole in the bolt or shaft underneath. This creates a mechanical lock that prevents the nut from loosening due to vibration or movement, ensuring that everything remains secured during operation.

While other options like a lock washer may be used with nuts to prevent them from loosening, they do not directly engage with the unique design of a castellated nut. A roll pin is primarily used for joining two components together and is not suitable for this application. A set screw, used to secure an object within or against another object, does not provide the locking mechanism needed for a castellated nut. Thus, utilizing a split pin is the best and most effective choice with a castellated nut to ensure proper fastening.