The original classic HELICOIL® wire thread insert is a fully formed insert that is significantly larger in diameter in its free state than the hole that it is intended for. It has to be pre-wound in the installation tool prior to installing and then when it is in position and the tool removed it expands, like a spring, to fit precisely into the threaded hole providing a hardwearing screw thread with the greatest tensional strengths higher than the original tapped hole.