Spark plugs are a mission-critical part of a gasoline engine's ignition system. Without them, there's nothing to ignite the air-fuel mixture in each cylinder.

Although the definition of spark-plug gap is intuitive for those who know what plugs are, we feel an explanation is good and necessary information for rookies, and a solid refresher for the OGs.

Japanese scientists are creating laser igniters that could one day replace spark plugs, resulting in better-performing, more efficient and cleaner-running engines.

Also, if you’re working on your own car, you bear some responsibility for making sure the parts you were given are correct.