Castle Nuts

Often called an axle nut as this is where they are most commonly found, a castle nut is a slotted hexagon nut with turrets on the top which resemble a castle wall. Castle nuts are used in conjunction with bolts that have holes in the end through which a locking pin can pass to lock the nut into position and prevent any further rotation. The locking pin is usually a split cotter pin, an R clip, a spring pin or a safety wire.

The diameter of the castellated section is slightly smaller than the main wrenching section of the nut (unlike a slotted nut where the diameter of the castellated section is the same as the main wrenching part).