Abstract: A spark plug that can reduce variation in a discharge point. The spark plug includes: a center electrode; a metal shell insulating and holding the center electrode; and a ground electrode including a base material having one end portion connected to the metal shell, and a tip connected to another end portion of the base material. The tip has a discharge surface opposed to the center electrode with a spark gap therebetween. The discharge surface has a quadrangular shape and is chamfered at four sides thereof. Only a first side which is one of the four sides is provided with a C chamfer.

Abstract: A spark plug including a ground electrode including a base material, a tip having a discharge surface, and a melt portion interposed over an entire area between the tip and the base material and joining the tip to the base material; and a center electrode with a spark gap formed between the center electrode and the discharge surface. The tip has, in an inner area surrounded by an outer peripheral portion of the tip, a thin portion in which a distance between the discharge surface and the melt portion is shorter than a distance between the discharge surface and the melt portion in the outer peripheral portion. The thin portion extends from a part of the outer peripheral portion to a part other than the part of the outer peripheral portion.

Abstract: A spark plug including a ground electrode including a base material, a tip having a discharge surface, and a melt portion interposed over an entire area between the tip and the base material and joining the tip to the base material; and a center electrode with a spark gap formed between the center electrode and the discharge surface. The tip has, in an inner area surrounded by an outer peripheral portion of the tip, a thin portion in which a distance between the discharge surface and the melt portion is shorter than a distance between the discharge surface and the melt portion in the outer peripheral portion. The thin portion extends from a part of the outer peripheral portion to a part other than the part of the outer peripheral portion.