This is a military spec stainless steel ball chain, the same as used by millions of military members to carry their dog tags as well as other odds and ends. It may be used to carry various components around your neck for quicker access,
I would caution that these should be carried under your shirt for security if possible when not actually in use since the chain can slip off over your head if you bend over too far. Alternatively, you can secure the ball chain through a belt loop and carry the gear in a pocket. The ball chain may also be used to improvise repairs. Note that while pretty strong, the ball chain will break if subjected to excessive force, so it designed to break before you are choked should it somehow become caught up and you fall.
5 Pack of 30" Chains