An ignition plug such as a spark plug or a glow plug configured to ignite an air-fuel mixture in an internal combustion engine includes a mark that is formed of an oxide film generated on the surface of a metal member or is formed of the metal member and the oxide film. The mark is formed by promoting formation of the oxide film on the surface of the metal member or removing the oxide film through radiation of a laser beam onto the surface of the metal member.

There is provided a spark plug testing kit for safe and convenient testing of petrol engines. The testing kit has a spark observation device within which a spark gap of a spark plug installed therein may be observed in use. The kit has a positive lead for connection to the engine distributor and an earth lead configured for connection to a spark plug opening engaging device. The spark plug engaging opening device comprises threading for turning into a spark plug socket of an engine block and defines an elongate male electrical connection nut standing proud therefrom over which a corresponding electrical connection of the earth lead may be easily and safely electrically connected. The spark plug engaging opening device further comprises exhaust ports through a side of the device for engine decompression during cranking.

There is provided a spark plug testing kit for safe and convenient testing of petrol engines. The testing kit has a spark observation device within which a spark gap of a spark plug installed therein may be observed in use. The kit has a positive lead for connection to the engine distributor and an earth lead configured for connection to a spark plug opening engaging device. The spark plug engaging opening device comprises threading for turning into a spark plug socket of an engine block and defines an elongate male electrical connection nut standing proud therefrom over which a corresponding electrical connection of the earth lead may be easily and safely electrically connected. The spark plug engaging opening device further comprises exhaust ports through a side of the device for engine decompression during cranking.

A method of inspecting a spark plug insulator that includes a collar portion, a rear body portion located in rear of the collar portion and a leg portion located in front of the collar portion. The inspection method includes: performing measurement of a distance in a radial direction of the insulator between an outer circumferential surface of the leg portion at a first measurement point and an outer circumferential surface of the any portion of the insulator other than the leg portion at a second measurement point, wherein the measurement is performed at a plurality of positions in a circumferential direction of the insulator with no contact to the measurement target; determining, as a circular runout, a difference between maximum and minimum values among measurement results of the distance; and making pass/fail judgment of the insulator based on the determined circular runout.

A method of inspecting a spark plug insulator that includes a collar portion, a rear body portion located in rear of the collar portion and a leg portion located in front of the collar portion. The inspection method includes: performing measurement of a distance in a radial direction of the insulator between an outer circumferential surface of the leg portion at a first measurement point and an outer circumferential surface of the any portion of the insulator other than the leg portion at a second measurement point, wherein the measurement is performed at a plurality of positions in a circumferential direction of the insulator with no contact to the measurement target; determining, as a circular runout, a difference between maximum and minimum values among measurement results of the distance; and making pass/fail judgment of the insulator based on the determined circular runout.

A spark plug has an electrode including a base portion and a tip joined to a specific surface that is a specific outer surface of the base portion, the tip forming a spark discharge surface. Respective relative positions of a plurality of points on an outer surface of a target portion of the electrode including the base portion and the tip joined to the base portion, which is a portion including at least a portion of the specific surface of the base portion and the tip, are identified to generate three-dimensional coordinate data representing the three-dimensional shape of the target portion. The coordinate data is analyzed to determine whether the target portion of the electrode includes a predetermined unintentional portion that is an unintended portion. An electrode including the unintentional portion is excluded from objects to be manufactured, and an electrode not including the unintentional portion is used to assemble the spark plug.

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 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.

An ignition apparatus for internal combustion engines is provided. The ignition apparatus is equipped with an ECU. The ECU monitors a path length of a discharge of a spark for a period of time in which a second circuit delivers or inputs energy in the form of a threshold value determination. When the path length has become too short, the ECU determines that ignition is expected to be delayed and then selects a special mode to control the delay of the ignition. The ECU increase a target value of an energy input amount. This enables the delay of ignition resulting from a short extension of the path length to be minimized. The ignition apparatus equipped with the second circuit to continue the discharge of sparks is, thus, capable of reducing a variation in ignition without the need for uniformly increasing the energy input amount.

A measuring device that includes a base having a base reference surface to which a workpiece reference surface is opposed, measures a gap in an axial direction between the base reference surface and the workpiece reference surface by use of a fluid flowing between the base reference surface and the workpiece reference surface, in a state where the workpiece reference surface is opposed to the base reference surface. Dice, a distance to which in the axial direction from the base reference surface is known, form the external thread on the axial portion toward a direction away from the flange portion through rolling. A calculation device obtains a target position, in the axial direction, of the workpiece to be disposed on the dice, on the basis of the known distance and the measured gap.