Spark plug for internal combustion engine

A spark plug for an internal combustion engine, comprising:

• a metal shell having an outer periphery formed with a mounting thread;
• a porcelain insulator fixedly secured to the metal shell on a central axis thereof with a distal end located outside the porcelain insulator;
• and
• a ground electrode joined to the metal shell and having an end spaced from the distal end of the center electrode to define therebetween a spark discharge gap;
• wherein the ground electrode includes a facing surface intersecting the central axis of the center electrode and having a width equal to or less than 1.4 mm;
• the ground electrode includes a noble metal chip supported on the facing surface at a position inward of a distal end of the ground electrode so as to protrude into the spark discharge gap;
• the noble metal chip has an outer diameter falling in a range equal to or greater than 0.4 mm and equal to or less than 1.0 mm;
• the noble metal chip has an axial length falling in a range equal to or greater than 0.3 mm and equal to or less than 1.5 mm;
• the distal end of the center electrode has an outer diameter falling in a range equal to or greater than 2 mm;
• the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface;
• and
• the ground electrode has sidewalls whose corners are formed with chamfered portions, respectively.