Definition & Function of Shackle

Shackles are load-bearing connecting devices with a removable pin. There are many different types of shackles, and they are collectively used to connect lifting slings, chain, rope to a load or to each other. Besides this, there are many other uses such as trailer hitches, marine applications, tie-down, and more. 

All shackles have four definitive parts. The bow is the curved part opposite the pin where the load is applied. The ears are the parts of the shackle body that support the pin, and the pin is usually a steel bolt that spans the two shackle ears. The shoulder is the part of the pin that makes contact against the ear when fully threaded. 

The most common shackles are anchor shackles and bow shackles. They have a rounded "O" shape and are able to accommodate multiple connections because of this. Other common shackle types are chain shackles and "D" shackles. These have a narrower "D" shape, and because of this should never be side loaded. There are three main pin types, screw pin, round pin, and bolt type. Screw pin shackles are convenient because they are easy to connect and disconnect, but should not be used for permanent installations. Round pin shackles have an unthreaded pin secured by a cotter pin. They are popular in tie-down applications but should not be used for overhead lifting or where side loading may occur. Bolt type shackles are more secure with a bolt and nut securing the shackle alongside a cotter pin. These can be used in place of both screw pin and round pin shackles. Because of the tightening nut and cotter pin these do not need to be tightened for every lift, and can be used for more permanent and long-term installations.