Explanation:

Castle nut:

• Slots are cut in a cylindrical collar provided on the top of the nut, thus overcoming the disadvantage of the slotted.
• Castle nuts are widely used in automobiles and locomotive engines to avoid sudden shock and vibration.

• The position of the nut can be locked using the split pin.
• A split pin is made from a steel wire of semicircular cross-section, bent as shown in the figure.
• It is inserted in a hole drilled in the bolt so that it exerts pressure on the top face of the nut to prevent it from turning.
• Split pins are designated by the nominal size, nominal length, the number of the Indian Standard, and the material.
• The nominal length is the distance from the underside of the eye to the end of the short leg.
• Split pins are used for locking slotted nuts, castle nuts, hexagonal nuts, clevis pins, etc., and are used in different ways.