Using Heli-Coil serrated aviation inserts is the only FAA approved method of repairing damaged spark plug threads. It is also the only method certified by engine manufacturers such as Teledyne-Continental and Textron-Lycoming. Serrated inserts, unlike regular inserts, require special tools to insert expand and stake them in place. These kits contain everything you will need including: piloted tap, insertion tool, offset and staking tool, expanding tool, 20 serrated inserts (10 each 1/2" and 13/16" long inserts), and complete instructions. 5 lbs (2.5Kg) shipping weight.