While castellated nuts are often referred to as slotted nuts, from a technical perspective, slotted nuts differ slightly from castellated nuts. Castellated nuts are formed with a round section at the top where the slots are located. Slotted nuts do not have this rounded modification. The flat sides of slotted nuts extend fully from the top to the bottom of the nut. Both castellated and slotted nuts are designed to use a pin (usually a cotter pin) that fits through the slots and through a hole in the screw to which the nut is attached. This pin prevents the nut from turning and loosening. Castellated nuts allow the cotter pin to be confined closer to the margins of the nut itself.