| 摘要 |
Provided is a spark plug to which excellent stress corrosion cracking resistance is imparted by means of appropriately specifying the nickel plating thickness of the inner surface of a metallic shell. The spark plug includes a metallic shell covered with a nickel plating layer and having a groove portion formed between a tool engagement portion and a gas seal portion and having an orthogonal-to-axis sectional area of 36 mm 2 or less. In a first configuration, as measured at a forward end of the inner circumferential surface of the groove portion, the nickel plating layer has a thickness of 0.3 µm to 2.0 µm; in a second configuration, a chromium-containing layer is formed on the nickel plating layer, and, as measured at the forward end of the inner circumferential surface of the groove portion, the nickel plating layer has a thickness of 0.2 µm to 2.2 µm; in a third configuration, a rust prevention oil is applied onto the nickel plating layer, and, as measured at the forward end of the inner circumferential surface of the groove portion, the nickel plating layer has a thickness of 0.2 µm to 2.2 µm; and in a fourth configuration, the chromium-containing layer is formed on the nickel plating layer, rust prevention oil is applied onto the chromium-containing layer, and, as measured at the forward end of the inner circumferential surface of the groove portion, the nickel plating layer has a thickness of 0.1 µm to 2.4 µm. |
