Abstract: A sole includes: a sole body; an elastic portion disposed adjacent to the sole body; a surrounding member that surrounds the elastic portion, and a pressing member. Tensile rigidity of the surrounding member in a thickness direction is higher than compression rigidity of the elastic portion in the thickness direction and higher than compression rigidity of the surrounding member in the thickness direction. An uncompressed thickness of the elastic portion in an uncompressed state is larger than an initial thickness of the surrounding member in an initial state. A reference thickness of the elastic portion and the surrounding member in an unloaded state is smaller than the uncompressed thickness of the elastic portion and larger than the initial thickness of the surrounding member.

Abstract: Spark plug has center electrode having leg portion extending in an axis direction, brim portion located at rear end side with respect to the leg portion and protruding outwards in a radial direction with respect to the leg portion and connecting portion connecting the leg portion and the brim portion; insulator having penetration hole and supporting the center electrode; and seal member filling the penetration hole and fixing the brim portion and the insulator. The center electrode satisfies “(D1-D2)/D1?0.06”, where a maximum value of a radius of the brim portion is D1, and a minimum value of the radius of the brim portion is D2, also satisfies “L2/L1?0.30”, where a size of the center electrode along the axis direction is L1, and a size along the axis direction from boundary between the connecting portion and the leg portion to a center of gravity of the center electrode is L2.

Abstract: Spark plug has center electrode having leg portion extending in an axis direction, brim portion located at rear end side with respect to the leg portion and protruding outwards in a radial direction with respect to the leg portion and connecting portion connecting the leg portion and the brim portion; insulator having penetration hole and supporting the center electrode; and seal member filling the penetration hole and fixing the brim portion and the insulator. The center electrode satisfies “(D1-D2)/D1 ? 0.06”, where a maximum value of a radius of the brim portion is D1, and a minimum value of the radius of the brim portion is D2, also satisfies “L2/L1 ? 0.30”, where a size of the center electrode along the axis direction is L1, and a size along the axis direction from boundary between the connecting portion and the leg portion to a center of gravity of the center electrode is L2.