Spark plug for internal combustion engine

An internal combustion engine spark plug comprising:

• a tubular ground electrode;
• a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode;
• and
• a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion, wherein
• the exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering an entire circumference of an outer peripheral surface of the insulator protruding portion from an outer peripheral side in a plug radial direction;
• and
• the exposed portion of the center electrode is formed within the ground electrode as viewed in the plug axial direction.

An internal combustion engine spark plug comprising:

• a tubular ground electrode;
• a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode;
• and
• a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion, wherein
• the exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering part of an outer peripheral surface of the insulator protruding portion in a plug circumferential direction from an outer peripheral side in a plug radial direction,
• at least a region, in which the second part is formed, of the insulator protruding portion in the plug circumferential direction has a step shape having an outer diameter that decreases in a stepwise manner toward the tip end side in the plug axial direction, and
• as viewed in the plug axial direction, the exposed portion of the center electrode is formed within the ground electrode.