Function: Function Used to fix severely cross damaged spark plug hole thread, cleaned up the threads without leaving scraps in the bore, no need pull cylinder head, no need coil insert. No Shavings Drop Into Engine Used grease on the threaded, so that it will trap any metal shavings within it and pull out with the device rather than drop into the cylinder chamber, not worry about stuff going down into the engine High Quality Material Made of high quality 42CrMo steel, its material is equivalent to 4140 steel, with high strength and toughness, good hardenability, no obvious tempering brittleness, high fatigue limit and multiple impact resistance after quenching and tempering, and good lowtemperature impact toughness. Therefore, it is more durable hard to damage, is a nice heavy and precise tool Tips Put it straight through the hole, expand it, back thread it 35x. Then reverse it in reverse, especially when it started getting tougher to turn, turning from side to side from time to time, at the same time, during the whole process, Just be sure to go slow. When u hit a hard patch, back it up a little then go forward again. After repeated operations, it is easy to remove the remaining material 12 Months Warranty We offer 12 months warranty, we will refund or replace if this 14mm back tap spark plug thread repair tool has any quality issue