Castle Nut: Also known as a slotted nut is a nut with notches cut into one end. Castle Nuts are used in low-torque applications, such as fastening a wheel bearing in place. A bolt or axle has one or two holes drilled through it's threaded end. The nut is then torqued properly, if the castle nuts slots are not aligned with the hole in the fastener, the nut is rotated to the nearest slot. The nut is then secured with a cotter pin or safety wire. Our selection below are plain and are not plated.