Patent ID: 8653725

Claim:
A spark plug for internal-combustion engines, comprising: a cylindrical insulator having an axial bore that penetrates in an axial direction; a center electrode inserted in one end of the axial bore; a terminal electrode inserted in another end of the axial bore; a cylindrical metallic shell provided on an outer circumference of the insulator; and a resistor made of at least a conductive material and glass, said resistor electrically connecting the center electrode to the terminal electrode in the axial bore, wherein the resistor is formed by heat-sealing of a resistor composition that contains at least the conductive material and glass powder, wherein the glass powder contains 35.0 mol % or more to 69.8 mol % or less silica dioxide, 15.0 mol % or more to 49.8 mol % or less boron oxide, 5.0 mol % or more to 20.0 mol % or less lithium oxide, wherein the glass powder contains at least one additive selected from a magnesium oxide, a calcium oxide, a strontium oxide, a barium oxide, a sodium oxide, an potassium oxide, a zinc oxide and a zirconium dioxide in a total of 2.6 mol % or more to 25.0 mol % or less, wherein the total content of lithium oxide and the additive(s) is 15.2 mol % or more to 45.0 mol % or less, and wherein a mol % ratio of the lithium oxide content to the total content of the additive(s) is between 1.3 and 5.0.