A metal wire that is fastened to the piece of equipment and a fixed point as a secondary attachment. This acts as a backup, preventing the item from falling if the primary attachment fails. A secondary attachment is a legal requirement.
Safety wire is common in the aircraft and racing industries as an extra precaution to keep vital fasteners from loosening and parts falling off. Safety wire is commonly .020, .025, .032 or .041 inches in diameter and usually made of stainless steel, but is also available in Monel and Inconel alloys for high temperature applications and copper for break-away applications. It is threaded through a hole drilled into a fastener or part, then twisted and anchored to a second fastener or part, then twisted again, usually with the aid of safety wire pliers.