Patent ID: 8288931

Claim:
A spark plug comprising: a center electrode extending along an axial direction; an insulator provided on a periphery of the center electrode; a cylindrical metal shell surrounding the insulator in a radial direction; and a ground electrode including a discharge surface perpendicular or substantially perpendicular to the axial direction, and forming a spark gap defined between the discharge surface and a leading end of the center electrode, wherein the center electrode and the ground electrode are not provided with a noble metal member, when defining a downward direction as a direction of the axial direction directing from the center electrode to the discharge surface of the ground electrode, and defining an upward direction as a direction of the axial direction opposite to the downward direction, and the ground electrode comprises: a base portion combined with the metal shell and positioned at the upward direction side of the discharge surface; and a distal end portion including the discharge surface and positioned at the downward direction side of the base portion while continuing from the base portion, wherein when defining a first direction as a direction perpendicular to the axial direction and directing from the base portion to the center electrode, defining a width of the center electrode viewed from the first direction as Da, and defining a width of the base portion viewed from the first direction as Db, Da and Db satisfies 0.87 â‰¦Db/Daâ‰¦0.92.