spark plugs for internal combustion engine of a motor vehicle

A spark plug (1) for the internal combustion engine of a motor vehicle, of essentially elongated general shape, comprising: - two coaxial electrodes: an inner electrode axis (D) called a central electrode (3) and an electrode called external cap (2) surrounding the central electrode (3) - an electrically insulating block called insulator (4) interposed between the central electrode (3) and the pellet (2), of annular shape and having a shoulder (5 ) annular characterized in that the insulator (4) has a groove (8) annular.