Patent ID: 7215069

Claim:
A spark plug comprising: a center electrode for spark discharge at its own leading end having a central axis; an insulating porcelain having an axial hole extending in a direction along said central axis of the center electrode, said porcelain holding the center electrode inside of the axial hole and having an outwardly projecting step portion; a metallic shell surrounding the insulating porcelain in the radial direction, for tightening and holding the outer circumference of the insulating porcelain, said shell having an inwardly projecting step portion; and an annular packing interposed between the step portion of the insulating porcelain and the step portion of the metallic shell for sealing engagement therewith, said packing formed of a material having a Young's modulus F (Pa) and said metallic shell formed of a material having a Young's modulus G (Pa) wherein 7.4×10 10 (Pa) is less than or equal to F is less than or equal to G minus 5×10 10 (Pa), and the tensile strength of the material of the packing is 400 MPa or more.