Abstract: A spark plug that prevents a decrease in strength of a member to which a mark is attached while ensuring a readability of the mark, and a method of manufacturing the spark plug. The spark plug is configured to ignite an air-fuel mixture in an internal combustion engine. The spark plug includes: a mark formed of an oxide film generated on a surface of a metallic member or is formed of the metallic member and the oxide film; and a coating material covering the whole mark and allowing transmission of light.

Abstract: A spark plug that prevents a decrease in strength of a member to which a mark is attached while ensuring a readability of the mark, and a method of manufacturing the spark plug. The spark plug is configured to ignite an air-fuel mixture in an internal combustion engine. The spark plug includes: a mark formed of an oxide film generated on a surface of a metallic member or is formed of the metallic member and the oxide film; and a coating material covering the whole mark and allowing transmission of light.

Abstract: In a cross section including a central axis, a value L/D obtained by dividing an axial length L of an overlap portion where a metal contact surface located on a metal shell and on which a packing is in contact with the metal shell overlaps a projection plane located on the metal shell and on which a contact surface located on an insulator and on which the packing is in contact with the insulator is projected in a direction orthogonal to the central axis by a difference D between a radius of an outer circumference of a tube portion at a connection position to a step portion and a radius of an outer circumference of a leg portion at a connection position to the step portion is 1.2 or more. This ensures the force of constraint in the radial direction provided by the packing on the insulator.

Abstract: In a cross section including a central axis, a value L/D obtained by dividing an axial length L of an overlap portion where a metal contact surface located on a metal shell and on which a packing is in contact with the metal shell overlaps a projection plane located on the metal shell and on which a contact surface located on an insulator and on which the packing is in contact with the insulator is projected in a direction orthogonal to the central axis by a difference D between a radius of an outer circumference of a tube portion at a connection position to a step portion and a radius of an outer circumference of a leg portion at a connection position to the step portion is 1.2 or more. This ensures the force of constraint in the radial direction provided by the packing on the insulator.