Shackles and clevises are U-shaped mechanical couplers shut by a pin or bolt. They attach a chain, cable rope or synthetic sling for rigging, towing and lifting. They’re constructed with several shapes, pin styles and strengths. The size is specified by the diameter of the body, not the size of the pin. Shackles are primarily used in construction, rigging and lifting. A clevis is utilized in less demanding applications such as farming and towing.