SPARK PLUG

摘要

This invention addresses the problem of providing a spark plug for which the central electrode is satisfactorily anchored within the shaft hole. This spark plug is equipped with: an insulating body having a shaft hole that extends in the axial direction, a first inner circumferential surface that forms the tip end of the shaft hole, a second inner circumferential surface that forms the rear end of the shaft hole and has an inner diameter greater than that of the first inner circumferential surface, and a ledge part connecting the first inner circumferential surface and the second inner circumferential surface; a central electrode that is formed by plastic processing, and has a large-diameter part that is supported by the ledge part, a protruding part that protrudes from the large-diameter part toward the rear end, and a columnar leg part that abuts the large-diameter part and protrudes in the space enclosed by the first inner circumferential surface; and a sealing part for the purpose of anchoring the central electrode within the shaft hole. When the diameter of a hypothetical cylinder having the minimum diameter capable of surrounding the aforementioned protruding part is A (mm), and the maximum diameter of the large-diameter part is B (mm), and the average diameter of the leg part in the space enclosed by the first inner circumferential surface is C (mm), and when C < A, then A - C = B - A.