Standard image data representing standard image including image of slit of a standard device is produced by photographing the standard device including the slit which includes a standard slit segment having a predetermined width. A width of the standard slit segment in the standard image is determined by analyzing the standard image data. Gap image data representing a gap image which is an image including an image of a discharge gap of a spark plug is produced by photographing the spark plug. A distance of the discharge gap in the gap image is determined by analyzing the gap image data. By using the distance of the discharge gap in the gap image and the width of the standard slit segment in the standard image, it is determined whether an actual distance of the discharge gap is within a predetermined allowable range or not.

A prechamber spark plug. The prechamber spark plug includes a central electrode and a ground electrode which are arranged in a prechamber, and a housing having a lateral hole, the ground electrode being arranged in the lateral hole in such a way that there is a gap area and a fastening area between the ground electrode and the housing.

A spark plug is provided which includes a cylindrical metal shell, a cylindrical porcelain insulator retained in the metal shell, a center electrode, and a ground electrode. The center electrode is disposed in the insulator with a head protruding outside a front end surface of the insulator. The ground electrode is joined to the metal shell and includes a gap-defining portion which faces a side surface of a side surface of the center electrode to define a spark gap and also faces the front end surface of the porcelain insulator to define a semi-surface discharge gap for burning off, for example, carbon deposits on the front end surface of the insulator.

Standard image data representing standard image including image of slit of a standard device is produced by photographing the standard device including the slit which includes a standard slit segment having a predetermined width. A width of the standard slit segment in the standard image is determined by analyzing the standard image data. Gap image data representing a gap image which is an image including an image of a discharge gap of a spark plug is produced by photographing the spark plug. A distance of the discharge gap in the gap image is determined by analyzing the gap image data. By using the distance of the discharge gap in the gap image and the width of the standard slit segment in the standard image, it is determined whether an actual distance of the discharge gap is within a predetermined allowable range or not.

Standard image data representing standard image including image of slit of a standard device is produced by photographing the standard device including the slit which includes a standard slit segment having a predetermined width. A width of the standard slit segment in the standard image is determined by analyzing the standard image data. Gap image data representing a gap image which is an image including an image of a discharge gap of a spark plug is produced by photographing the spark plug. A distance of the discharge gap in the gap image is determined by analyzing the gap image data. By using the distance of the discharge gap in the gap image and the width of the standard slit segment in the standard image, it is determined whether an actual distance of the discharge gap is within a predetermined allowable range or not.

A spark plug is provided which includes a cylindrical metal shell, a cylindrical porcelain insulator retained in the metal shell, a center electrode, and a ground electrode. The center electrode is disposed in the insulator with a head protruding outside a front end surface of the insulator. The ground electrode is joined to the metal shell and includes a gap-defining portion which faces a side surface of a side surface of the center electrode to define a spark gap and also faces the front end surface of the porcelain insulator to define a semi-surface discharge gap for burning off, for example, carbon deposits on the front end surface of the insulator.

A spark plug including a pre-chamber for an engine is provided. The spark plug extends along a spark plug longitudinal axis. The spark plug includes a first cylindrical structure having a wall defining a bore. An electrode is positioned inside the bore such that the electrode is spaced apart from the wall to define at least one electrode spark gap. The spark plug further includes a second cylindrical structure configured to receive the first cylindrical structure. The second cylindrical structure has one or more access apertures configured to facilitate access to the wall of the first cylindrical structure, wherein a plane perpendicular to the spark plug longitudinal axis passes through the electrode spark gap and intersects the one or more access apertures.

A method of manufacturing a spark plug includes: mounting a metal shell on an assembly body of a temporary insulator and a temporary center electrode; causing discharge to occur between the temporary center electrode and the metal shell by applying a voltage across the metal shell and the temporary center electrode and capturing, while the discharge is occurring, an image of a range including the temporary center electrode, the temporary insulator, annular space which is present between the temporary insulator and the metal shell and has an opening on the front end side, and the metal shell; and determining whether or not the form of the inner circumferential surface of the metal shell is a predetermined form.

A surge protection component with a main body which has at least one inner electrode arranged between two ceramic layers, wherein the at least one inner electrode is set back from at least one lateral face of the main body, wherein a gas-filled cavity is provided between the at least one inner electrode and the at least one lateral face, and wherein an outer electrode is respectively arranged on two mutually opposite lateral faces of the main body. According to a further aspect, the present invention relates to a method for producing a surge protection component.

A surge protection component with a main body which has at least one inner electrode arranged between two ceramic layers, wherein the at least one inner electrode is set back from at least one lateral face of the main body, wherein a gas-filled cavity is provided between the at least one inner electrode and the at least one lateral face, and wherein an outer electrode is respectively arranged on two mutually opposite lateral faces of the main body. According to a further aspect, the present invention relates to a method for producing a surge protection component.