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.
DPTOOL 12mm Back Tap Spark Plug Thread Repair Tool M12x1.25 Thread Chase Tap ...
DPTOOL 12mm Back Tap Spark Plug Thread Repair Tool M12x1.25 Chase
DPTOOL 14mm Back Tap Spark Plug Thread Repair Tool M14x1.25 Chase M14
DPTOOL 14mm Back Tap Spark Plug Thread Repair Tool M14x1.25 Chase
