Patent ID: 7230369

Claim:
A spark plug comprising: a metal shell having a first end and a second end, the metal shell also having a threaded portion on an outer periphery thereof; an insulator having a first end and a second end, the insulator also having a bore formed therein, the insulator being fixed in the metal shell so that the first end of the insulator protrudes from the first end of the metal shell and the second end of the insulator protrudes from the second end of the metal shell; a center electrode secured in the bore of the insulator, the center electrode having a first end protruding from the first end of the insulator and a second end; a ground electrode joined to the first end of the metal shell so that the ground electrode is opposed to the center electrode through a spark gap; a terminal having a first end and a second end, the terminal being partially inserted into the bore and fixed to the insulator so that the first end of the terminal electrically connects to the second end of the center electrode and the second end of the terminal protrudes from the second end of the insulator; and wherein an absolute value of a diameter difference represented by |B−A| is equal to or less than 0.6 mm, where A is a maximum diameter of a protruding portion of the terminal, protruded from the second end of the insulator, and B is a diameter of a protruding portion of the insulator, protruded from the second end of the metal shell.