Extension spark plug

1. A spark plug comprising:

an electrode extension having both an upper portion for being selectively connected to an energy source and a lower portion;

a firing electrode substantially axially aligned and in communication with the lower portion of the electrode extension;

a ground plate situated proximate to the firing electrode so as to define a spark gap between the firing electrode and the ground plate;

a sleeve insulator surrounding the electrode extension and having a first end and a second end and a central section;

an upper insulator surrounding both the upper portion of the electrode extension and the first end of the sleeve insulator so as to be in contact with the sleeve insulator;

a lower insulator surrounding both the lower portion of the electrode extension and the second end of the sleeve insulator so as to substantially be in contact with the sleeve insulator;

a metallic conduit surrounding the upper and lower insulators and the sleeve insulator; and

wherein the upper and lower insulators are spaced axially from one another across the central section of the sleeve insulator such that the central section is exposed directly to the surrounding metal conduit.

2. A spark plug as set forth in claim 1 , the spark plug further comprising a metallic contact button that is substantially axially aligned and in contact with the upper portion of the electrode extension.

3. A spark plug as set forth in claim 2 , wherein the metallic contact button includes threads for engaging threads defined in the upper portion of the electrode extension.

4. A spark plug as set forth in claim 2 , the spark plug further comprising an end bushing that is secured to an upper end of the metallic conduit for thereby connecting an electrical conductor to the contact button.

5. A spark plug as set forth in claim 1 , wherein the upper insulator has a plurality of portions having different diameters.

6. A spark plug as set forth in claim 1 , wherein the lower insulator has a plurality of portions having different diameters.

7. A spark plug as set forth in claim 1 , wherein the upper insulator includes a cavity for receiving the first end of the sleeve insulator.

8. A spark plug as set forth in claim 1 , wherein the lower insulator includes a cavity for receiving the second end of the sleeve insulator.

9. A spark plug as set forth in claim 1 , wherein the lower insulator at least partially surrounds the firing electrode.

10. A spark plug as set forth in claim 1 , the spark plug further comprising a shell in which both the firing electrode and the lower insulator are at least partially retained.

11. A spark plug as set forth in claim 10 , wherein the shell further retains a radio-frequency suppressor device.

12. A spark plug as set forth in claim 10 , wherein the ground plate is attached to the shell.

13. A spark plug as set forth in claim 1 , wherein the ground plate surrounds the firing electrode and includes a plurality of prongs that extend toward the firing electrode.