Spark plug

A spark plug comprising:

• an insulator extending along an axial line from a distal side toward a proximal side;
• and
• a cylindrical metal shell provided around an outer periphery of the insulator,
• wherein the metal shell includes, on an inner periphery of the metal shell,
• a ledge portion including a proximally oriented surface and a distally oriented surface, the proximally oriented surface being in contact with the insulator directly or with another member in between, the distally oriented surface being located on the distal side relative to the proximally oriented surface;
• a first surface extending from the distally oriented surface toward the distal side;
• and
• a second surface extending from the proximally oriented surface toward the proximal side,
• wherein, in a section containing the axial line,
• an angle A formed between the distally oriented surface and the first surface and an angle B formed between the proximally oriented surface and the second surface have a relationship of A≤1.15B, with the angle A being greater than or equal to 90° and the angle B being greater than or equal to 90°, and
• wherein the insulator includes a third surface that faces the first surface from a radially inner side.