Patent ID: 7365480

Claim:
A spark plug comprising: an insulator having a through hole in an axial direction of said spark plug and comprising alumina ceramics; a center electrode partially inserted in a front end of the through hole; an external terminal partially inserted in a rear end of the through hole; and a conductive seal provided between said external terminal and said center electrode in said through hole, wherein said conductive seal contains base glass, a conductive filler and from 0 to 10 weight % of an insulating filler, said base glass contains: a Si component in an amount of from 55 to 65 weight %, in terms of SiO 2 , a B component in an amount of from 22 to 35 weight %, in terms of B 2 O 3 , a Ca component in an amount of from 0.2 to 2 weight %, in terms of CaO, an Al component in an amount of 2 weight % or less, in terms of Al 2 O 3 , and a Na component and a K component in a total amount of from 4 to 8 weight %, in terms of Na 2 O and K 2 O, respectively, and said base glass contains both said Na component and said K component.