There’s nothing wrong with using Heli Coil products for repairing damaged spark plug threads as long as you use the correct item for the application. Standard Heli Coils are nothing more than a wound piece of wire and are meant for repairing internal threads of bolt holes etc. Spark plug threads are different and require the use of a Heli Coil Spark Plug Insert to do the job right. When installed correctly, believe me, they will not come out with the plug and have much better sealing and heat transfer properties than a standard Heli Coil thread repair insert.
The Kit.
Various size inserts.
Standard thread repair inserts. See the difference?
