Ngk Spark Plug Company, Limited

Hiroyuki Odo

Naofumi Yamamura

Kuniyuki Ishii

Naoya Onoda

A spark plug includes a metal shell, an insulator, a center electrode, and a ground electrode. At least one of the center electrode and the ground electrode includes a projection having a columnar shape. The projection projects toward the other of the center electrode and the ground electrode and forms the discharge gap. A portion of a side surface of the projection has a recess. A melted portion is formed by melting the noble metal tip and an electrode base material. The recess is formed in the melted portion. 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, 0.05 mm&#x2266;D&#x2266;0.3&#xd7;R is satisfied.

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Kounan, Japan

Hiroyuki Odo