Cracked threaded bolt hole have always been difficult to repair because of the spreading force exerted when the bolt or threaded device is torqued. Standard thread repair insets and coils are ineffective in these situations ie. stripped, leak blind hole, out of round, cracked, broken as they can even make the problem worse by removing material around the threaded hole.
In such situation, we install thread repair insert to restore both the needed strength and the new inner thread at the same time. The threads on the outside of the insert are the same as metal stitching pin, which can be installed very close to the edge without weakening the parent metal.