- Specially designed to repair damaged spark plug threads on modern 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. - Size: 14mm. - Length: 138mm. - 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.