A number of components are involved in successful overhead lifting, including lifting shackles. Such shackles can be used in a variety of different manners in the overhead lifting process, including connecting extra slings together or attaching a load to a sling. Shackles are constructed of a curved piece of metal that is secured with a bolt or a pin that runs across the opening. In choosing the right type of shackle for the application, it should be understood that there are four basic types of lifting shackles. Those four types of shackles include bolt anchor, screw pin, bolt chain, and screw pin chain. As is the case when choosing many types of rigging and lifting equipment, it is important to pay attention to the working load limit and the size of the shackle in order to choose the best product for the job. Lifting shackles are graded based on the mean stress that can be handled at the minimum breaking load. This is similar to the way in which chain slings and chains are graded. To make things simple, it should be kept in mind that the higher the grade of the shackle, the greater capacity the shackle will have for a particular size. Sizes can range anywhere from 3/16 of an inch up to 4 inches. Working load limits are typically given in terms of tons. A 3/16-inch shackle can typically only handle a working load limit of 1/3-ton, while a 4-inch shackle can accommodate a working load limit of 150 tons. Under no circumstances should the working load limit of a lifting shackle be exceeded. Attempting to do so is a recipe for disaster. The dimensions of the shackle should also be taken into consideration. Depending on the application, the dimensions of the shackle can also be a limiting factor. For instance, when connecting two slings, it is important to ensure that the shackle is large enough to fit onto the crane hook while still accommodating the two slings.