Castle nuts are useful when you need the power of a locking nut without the permanent commitment. As long as the castellated nut is secured with a cotter pin, it is not likely to move due to movement of the machine or vibration. It can also be used over and over again.

What are castellated nuts used for?

A castellated nut, also known as a castle nut, has three notches in one end, giving an appearance similar to the crenellated battlements of a castle. Castellated nuts are a positive locking device that's used to ensure that the nut remains affixed and resists vibration.

What must be used in conjunction with a castellated nut?

In addition to a bolt, they require the use of a pin. After tightening a castellated nut onto the end of a bolt, a pin is inserted through the center. The pin will essentially hold the castellated nut in place. It will run through the center of the nut and the center of the bolt to which the nut is attached.