Abstract: A spark plug including a ground electrode body and an electrode tip that is resistance welded to the ground electrode body and that has a discharge surface. In a specific sectional plane, a welding surface is located in the first direction from an outer surface of the ground electrode body. The welding surface includes a flat portion whose distance to the point P1 in the first direction is 0.05 mm or smaller, and when a point E1 and a point E2 are defined as ends of the flat portion and a second direction is defined as a direction from the point E2 toward the point E1, in the second direction from the point E1, a distance between the welding surface and the discharge surface in the first direction is smaller than a distance between the discharge surface and the point E1 in the first direction.

Abstract: A spark plug including a ground electrode body and an electrode tip that is resistance welded to the ground electrode body and that has a discharge surface. In a specific sectional plane, a welding surface is located in the first direction from an outer surface of the ground electrode body. The welding surface includes a flat portion whose distance to the point P1 in the first direction is 0.05 mm or smaller, and when a point E1 and a point E2 are defined as ends of the flat portion and a second direction is defined as a direction from the point E2 toward the point E1, in the second direction from the point E1, a distance between the welding surface and the discharge surface in the first direction is smaller than a distance between the discharge surface and the point E1 in the first direction.

Abstract: A spark plug includes an insulator extending along an axis and a metal shell provided on the outer periphery of the insulator. The metal shell includes a thread portion for threadedly engaging with a mounting hole of an internal combustion engine and a seat portion having a tapered surface whose outer diameter decreases gradually toward a leading end side. The tapered surface contacts with a bearing surface of the internal combustion engine when the thread portion is engaged with the mounting hole. Annular protruding portions or a helical protruding portion are formed within a range on the tapered surface from an outermost peripheral portion to a part forming an outer diameter occupying 95% of the diameter of the outermost peripheral portion. The arithmetic mean roughness of a surface of the tapered surface within the range is set to 1-5 ?m on a section including the axis.

Abstract: A spark plug includes an insulator extending along an axis and a metal shell provided on the outer periphery of the insulator. The metal shell includes a thread portion for threadedly engaging with a mounting hole of an internal combustion engine and a seat portion having a tapered surface whose outer diameter decreases gradually toward a leading end side. The tapered surface contacts with a bearing surface of the internal combustion engine when the thread portion is engaged with the mounting hole. Annular protruding portions or a helical protruding portion are formed within a range on the tapered surface from an outermost peripheral portion to a part forming an outer diameter occupying 95% of the diameter of the outermost peripheral portion. The arithmetic mean roughness of a surface of the tapered surface within the range is set to 1-5 ?m on a section including the axis.

Abstract: A spark member (70) is formed by joining a noble metal member (71) and an intermediate member (75) and is provided in a spark discharge gap between a center electrode and a ground electrode (30). A bottom surface (80) of the intermediate member (75) is resistance-welded to an inner surface (33) of the ground electrode (30), and a weld metal zone (73) is formed in the region of joint therebetween. As viewed on the section of the spark member (70) which contains a centerline (Q), the weld metal zone (73) is reliably formed within the range of the length (D) of a columnar portion (76) as measured along a direction orthogonal to the projecting direction of the spark member (70) and has a length (d) of at least 0.1 times (10% of) the length (D).

Abstract: A spark member (70) is formed by joining a noble metal member (71) and an intermediate member (75) and is provided in a spark discharge gap between a center electrode and a ground electrode (30). A bottom surface (80) of the intermediate member (75) is resistance-welded to an inner surface (33) of the ground electrode (30), and a weld metal zone (73) is formed in the region of joint therebetween. As viewed on the section of the spark member (70) which contains a centerline (Q), the weld metal zone (73) is reliably formed within the range of the length (D) of a columnar portion (76) as measured along a direction orthogonal to the projecting direction of the spark member (70) and has a length (d) of at least 0.1 times (10% of) the length (D).