Abstract: A noble metal tip of a grounding electrode is inclinedly disposed with respect to a noble metal chip of a central electrode by an angle &agr; so that a discharging gap is narrow at a side closer to one end of the grounding electrode and wide at the opposite side closer to the other side of the grounding electrode. When the discharging gap has expanded to a certain extent due to exhaustion of the noble metal tips of the electrodes, the re-gapping adjustment is performed to decline or push the noble metal tip of the grounding electrode toward the noble metal tip of the central electrode so as to decrease the angle &agr;. Thus, the discharging gap can be adjusted to an adequate value.

Abstract: A spark plug having a glaze layer on the insulator thereof, wherein the glaze layer has a reduced Pb content, is capable of being fired at a relatively low temperature, exhibits excellent insulation properties, and can have a smooth surface.

Abstract: A cathode ray tube has an electron gun including an indirectly heated cathode structure having a heater therein. The heater has a major heating portion formed of a spirally wound heating wire and two leg portions connected to opposite ends of the major heating portion. The two leg portions are welded to electrical conductors for applying voltages thereto at portions in the vicinity of open ends of the two leg portions, respectively, and the heater is covered with an insulating film except for the portions for welding. The two leg portions includes at least five layers of winding formed by spirally winding heating wires identical with the heating wire of the major heating portion, and the numbers of turns per unit length in each of the at least five layers of winding are smaller than a number of turns per unit length of the heating wire of the major heating portion.