Patent ID: 10931087

Abstract:
An ignition plug includes a tubular insulator, a metallic shell disposed around the outer circumference of the insulator, a center electrode disposed in an axial hole of the insulator, and a ground electrode connected to the forward end of the metallic shell and facing the center electrode. The metallic shell has a threaded portion to be engaged with an internal combustion engine. The relational expression Ss/(Sa+Sb)≥2.6 is satisfied, where Ss is the surface area of an outer circumferential surface of the metallic shell extending from the rear end of the threaded portion to the forward end of the threaded portion, Sa is the surface area of that portion of the metallic shell which is to be exposed to combustion gas of the internal combustion engine, and Sb is the surface area of that portion of the insulator which is to be exposed to the combustion gas.