By its very nature construction involves very large and heavy things. It can mean heavy materials, pre-fabricated components or equipment of all shapes and sizes to name just a few. Often these items need to be hoisted, dragged, or lowered to where they are needed. Shackles can provide an excellent way to facilitate these operations.
For example, a screw pin shackle is often used in conjunction with chains or slings for rigging loads to be lifted by a crane. Screw pin shackles allow the rigger to quickly but securely attach lifting slings to the crane or other lifting equipment. As its name implies these shackles incorporate a threaded anchor pin that can be firmly attached to the shackle and still be decoupled without the use of any tool.
A more permanent type of shackle is the bolt type shackle. This type of shackle differs from the screw pin shackle because it utilizes a threaded bolt for its anchor pin. A nut is required to then firmly secure the pin to the shackle. Often this type of shackle has a cotter pin that is used on the outside of the nut for further security against the pin coming out. The advantage of this type of shackle is its inherent permanent attachment. The disadvantage is it requires tools to disengage the pin from the shackle.
Regardless of the type of shackles the uses for them are nearly endless. In addition to the afformentioned use in rigging operation the shackle is versatile in making a connection point that otherwise would not be possible. For example, if a chain needs to be connected to a piece of equipment and there are no hooks or loops available a shackle pin can be inserted into a hole in the frame thus providing a place to run a chain.