US Patent 7315110 Spark plug with easy-to-recognize identification marks

A spark plug according to the invention has a length and an outer side surface. The outer side surface includes a plurality of closed band-shaped regions arranged in the lengthwise direction of the spark plug, within each of which a plurality of identical marks, which represent the same piece of information concerning the spark plug, are formed at predetermined intervals in a circumferential direction of the spark plug. Further, the marks within each of the regions represent the piece of information different from that represented by the marks within any other one of the regions, and each of the marks within each of the regions is aligned in the lengthwise direction of the spark plug with one of the marks within any other one of the regions. With such formation of marks, the spark plug can be accurately identified without rotating it to a specific position during the identification process.