Sealey MS002 Reverse Action Spark Plug Thread Chaser 12mm

Specially designed to repair damaged spark plug threads on modern petrol engines.
Unique design allows the tool to be passed through the plug thread into the combustion chamber, then expanded to the correct size starting on the inner, undamaged threads.
Traditional thread restorers rely on luck for the restored and undamaged threads to align.
The first letter(s) of a Denso, NGK and Bosch plug code is the thread size identification. For Champion brand the second letter(s) of a plug code is the thread size identification.