What is the purpose of using cotter pins with shackles?

Using cotter pins with shackles serves the critical purpose of securing the pin in place. In rigging applications, shackles are often used to connect two components, such as a chain to a load or to an anchor point. The pin typically holds the shackle together, but without a cotter pin or similar locking mechanism, the pin could loosen or fall out under load or during movement, potentially leading to a failure of the rigging setup.

By inserting a cotter pin through the hole in the pin of the shackle, it effectively prevents the pin from rotating or disengaging. This security measure ensures the integrity of the connection and helps maintain the safety of the lifting operation. This is particularly crucial in industrial rigging, where the risks associated with dropped loads or equipment failure can be significant.

The other options, while they pertain to rigging and equipment use, do not accurately reflect the primary function of cotter pins in this context.