Patent attributes
A spark plug includes an insulator having an axial hole formed in a direction of an axis, a center electrode held in one end side of the axial hole, a metal terminal held in the other end side of the axial hole, an electrical connection part arranged to establish electrical connection between the center electrode and the metal terminal within the axial hole, and a metal shell disposed around an outer circumference of the insulator and having a thread portion formed on at least a part of an outer circumferential surface thereof. The electrical connection part has a resistor, and a conductive seal layer provided between the resistor and the center electrode to seal and fix the insulator and the center electrode together. In a half or more of a region in which the seal layer is provided in the direction of the axis, the spark plug satisfies predetermined conditions.
