Patent ID: 8716924

Claim:
A spark plug comprising: a tubular ceramic insulator having an axial bore extending therethrough in an axial direction; a center electrode disposed at a forward end portion of the axial bore; and a metallic shell provided around the ceramic insulator; the spark plug being characterized in that: the metallic shell has: a tool engagement portion projecting outward and having a polygonal orthogonal-to-axis sectional shape; a gas seal portion projecting outward; and a groove portion formed between the tool engagement portion and the gas seal portion and having an orthogonal-to-axis sectional area of 36 mm 2 or less; the metallic shell is covered with a nickel plating layer; and as measured at a forward end of an inner circumferential surface of the groove portion, the nickel plating layer has a thickness of 0.3 μm to 2.0 μm.