Fastening irons, also known as SHACKLES, are a type of metal device used to secure objects together. They are typically composed of two parts, a hinged loop and a locking mechanism, and are commonly used in the construction industry to join two pieces of metal together. SHACKLES are also used in the maritime industry to secure ships and boats to docks or other vessels. In addition, they are often used in the security industry to restrain prisoners.