Patent ID: 9660423
Date: 2017-05-23
CPC Classifications: H01T

Claim:
1. A spark plug comprising: an insulator including an axial hole extending in an axial direction and a flat portion located at a rear end; a terminal nut disposed at a rear end of the axial hole and having a contact surface that is in contact with the flat portion; and a tubular metallic shell holding the insulator therein, wherein an outside diameter of the insulator at a rear end of the metallic shell is smaller than or equal to 8 mm, wherein a contact area between the flat portion of the insulator and the contact surface of the terminal nut is smaller than 10 mm wherein the terminal nut includes a projecting portion that is adjacent to a rear end of the contact surface and in which an outside diameter of the terminal nut gradually increases toward a rear side in the axial direction and then gradually decreases, and wherein a difference between a maximum outside diameter of the projecting portion and the outside diameter of the terminal nut at a rear end of the projecting portion is smaller than or equal to 0.2 mm.