Patent ID: 7432641
Filing Date: 2008-10-07
Classification: B28B,H01T

Abstract:
1. A spark plug comprising an insulator having a bore extending in an axial direction and holding a center electrode for generating spark discharge in a front end portion of the axial bore and a terminal electrically connected to the center electrode, at a rear end portion of the axial bore, wherein the axial bore of the insulator comprises a large diameter portion continuous with an opening located at a rear end of the axial bore and a small diameter portion continuous with a front end of the large diameter portion and smaller in diameter than the large diameter portion, and wherein an axial length A in mm of the insulator, an outside diameter B in mm of a rear trunk portion located rearward of a portion of the insulator having a maximum outside diameter, a diameter C in mm of the large diameter portion, an axial length D in mm of the large diameter portion, and a diameter E in mm of the small diameter portion satisfy the following inequalities: