Spark plug

A spark plug comprising:

• a center electrode having a leg portion extending in an axis direction along an axis of the spark plug, a brim portion located at an axis direction rear end side with respect to the leg portion and formed so as to protrude outwards in a radial direction with respect to the leg portion and a connecting portion connecting the leg portion and the brim portion;
• an insulator having a penetration hole formed along the axis direction and supporting the center electrode in the penetration hole;
• and
• a seal member filling the penetration hole and fixing the brim portion and the insulator, and wherein
• the insulator has
• a large diameter portion located at an axis direction rear end side of the insulator;
• a small diameter portion located at an axis direction top end side with respect to the large diameter portion, a diameter of the penetration hole at the small diameter portion being smaller than a diameter of the penetration hole at the large diameter portion;
• and
• a step portion connecting the penetration hole at the large diameter portion and the penetration hole at the small diameter portion and supporting the connecting portion, and
• the center electrode satisfies “(D1-D2)/D1 ≤ 0.06”, where a maximum value of a radius of the brim portion on a cross section including the axis is D1, and a minimum value of the radius of the brim portion on the cross section is D2, and
• the center electrode also satisfies “L2/L1 ≤ 0.30”. where a size of the center electrode along the axis direction on the cross section is L1, and a size along the axis direction from a boundary between the connecting portion and the leg portion to a center of gravity of the center electrode is L2.