SPARK PLUG

原文（中国語）

A spark plug includes an insulator including a step portion; a center electrode, and a metal shell being disposed around an outer periphery of the insulator and including an inner peripheral surface. The metal shell includes a threaded portion; a seating portion including a seating surface provided on the rear-end side of the threaded portion; and a retaining portion provided on the inner peripheral surface, the retaining portion retaining the step portion. The spark plug satisfies V/(R·L)≤0.0170, where V (mm) is a capacity of a space that is located on the front-end side of the retaining portion and inside the inner peripheral surface including the retaining portion and that excludes the center electrode and the insulator, R (mm) is an outer diameter of the threaded portion, and L (mm) is a distance from a front end of the metal shell to the seating surface.