When the chains pair-up, key goes with lock; hook with eye.

Again let us imagine that the key is damaged - maybe this time the links are also broken.  Maybe the key is just damaged in particularly bad way.  In any case, the short patch repair won't work.

The key has been damaged.

A section of chain will have to be cut out. The cell will then use the second strand as a template for installing a replacement section. In this example two links and two code symbols have been removed.

A long piece has been removed.

The gap is then filled in with a long patch including the missing key and lock.  The second strand will be used as a template for the repair.

When the chains pair-up, key goes with lock; hook with eye.

Sometimes as many as 10 links and symbols will be removed to make sure that the damaged section is completely replaced. As with short patch repair, a broken chain can be fixed this way or even damage where a code symbol and a chain link are damaged near each other.