Igniter plug

In combination with an igniter plug of the type having an inner elongated electrode having a front portion and a rear portion;

• an elongated insulator disposed around at least a portion of the electrode, said insulator having a front portion, a rear portion, and an axial passage extending through said insulator and having a portion of the inner electrode mounted therein;
• an outer elongated electrode comprising a metal shell mounted on the intermediate elongated insulator and disposed around the electrode and electrically isolated therefrom by the insulator, said metal shell having a rear portion and a front end portion which is arranged to provide a spark gap with the end of the front portion of said electrode;
• means for mounting the elongated insulator within said metal shell;
• means for providing a pressure-tight seal between said inner electrode, said elongated insulator and said metal shell;
• a forward insulator electrically isolating said forward portion of said outer shell from the forward portion of said inner electrode and being separated by an air space from said inner electrode;
• and means for mounting the forward portion of said inner electrode to the forward portion of said elongated insulator, the improvement wherein said last means comprises:
• a metal sleeve telescopically mounted to said inner electrode in the front portion of said insulator passage, said metal sleeve comprising a single piece of metal having a central passage that includes a first passage portion having a large cross sectional area and a second passage portion having a small cross sectional area connected together by a third passage portion, the inside surface of said second passage portion in contact with said electrode extending therethrough and the outside surface of said first passage portion in contact with said insulator passage.