Spiral inserts are inserts made of coiled wire. A spiral coil made of diamond shaped stainless steel or phosphor bronze wire is screwed into a threaded hole to form a matching internal thread for screws or studs. These inserts provide a convenient method for repairing peeled threads and are also used to provide stronger threads in soft materials such as aluminum, zinc die castings, wood, magnesium, etc. than the base material involved in direct tapping. Another common common name is Threaded Insert (STI), although many users use a prominent brand name to refer to them, the registered trademark Heli Coil. Applications include engine cylinder head repairs after unintentionally over tightening spark plugs or thread misalignment causing socket threads to fall off. There is a kit with matching taps and coils for this purpose. The diameter plate in the photo is the driver handle foot, which is used to clamp the key that drives the coil in place with an action pliers. After installation, it is discarded.
