The invention relates to a
spark plug for a gas-fired
internal combustion engine, and Includes a metallic body, with an insulator fastened in the body. A central
electrode, leads through the insulator and includes a protruding end of a
precious metal alloy. An annular ground
electrode is fastened to the body and surrounds the end of the central
electrode which, at the inside thereof facing the central electrode is provided with a
precious metal or with a
precious metal alloy. The mutually facing surfaces of the central electrode and ground electrode formed by the precious
metal or the precious
metal alloy are coaxially disposed cylinder surfaces. A cap is provided and attached to the body and which, after installation of the
spark plug into a
combustion chamber of the
internal combustion engine, shields the central electrode and the ground electrode from the
combustion chamber. Together with the body of the
spark plug, the central electrode forms an ante-chamber, in which the central electrode and the ground electrode are disposed. The cap having at least one opening, which enables a
gas exchange between the ante-chamber and the space outside of the ante-chamber. According to the invention, a deviation of the cylinder surfaces from the ideal cylinder geometry is less than +−20 μm, and a deviation of the positions of the axes of the cylinder surfaces from their ideal coaxial position is less than +−50 μm.