Patent ID: 9716370
Date: 2017-07-25
CPC Classifications: H01T

Claim:
1. A spark plug comprising: a metal shell having a tubular shape; an insulator having an axial hole that extends along an axial line, at least a portion of a periphery of the insulator being held by the metal shell; a center electrode disposed in the axial hole; and a ground electrode that is fixed to the metal shell and that forms a discharge gap between the ground electrode and the center electrode, wherein at least one of the center electrode and the ground electrode includes a projection having a columnar shape, the projection projecting toward the other of the center electrode and the ground electrode and forming the discharge gap, wherein only a portion of an entire periphery of a side surface of the projection has a recess, wherein the projection includes wherein the recess is formed in the melted portion, and wherein, when D is a depth of the recess from a side surface of the noble metal tip and R is a diameter of the noble metal tip, following condition (1) is satisfied: