Patent ID: 8890396

Claim:
A spark plug for a gas-fired internal combustion engine, the spark plug comprising: a metallic body; an insulator fastened in the body; a central electrode leading through the insulator and having a solid piece made from a precious metal or a precious metal alloy attached at an end of the central electrode and protruding beyond the insulator, the solid piece having a cylindrical surface, a center point, and a longitudinal axis where the cylindrical surface circumferentially extends around the center point of the solid piece and the longitudinal axis is aligned with the center point of the solid piece, wherein the cylindrical surface of the solid piece is an abrasively ground surface; a ground electrode fastened to the body and having an annular sleeve made from a precious metal or precious metal alloy and surrounding the solid piece of the central electrode, the annular sleeve having an inner cylindrical surface, a center point, and a longitudinal axis where the inner cylindrical surface circumferentially extends around the center point of the annular sleeve and the longitudinal axis is aligned with the center point of the annular sleeve, wherein the inner cylindrical surface of the annular sleeve is a drawn surface and the mutually facing cylindrical surfaces of the solid piece and the annular sleeve are coaxially disposed cylinder surfaces; and a cap attached to the body for shielding the central electrode and the ground electrode upon installation of the spark plug into a combustion chamber of the internal combustion engine and together with the body of the spark plug forming an ante-chamber for receiving the central electrode and the ground electrode, the cap having at least one opening for enabling a gas exchange between the ante-chamber and a space outside of the ante-chamber, wherein a deviation between the center point of the solid piece and the center point of the annular sleeve is less than +−20 μm, and a deviation between a position of the longitudinal axis of the solid piece and a position of the longitudinal axis of the annular sleeve is less than +−50 μm.