When considering the basic construction of the spark plug, there have been no profound changes over the past 50 years. Like before, the spark plug is comprised of a metal core which is housed in a ceramic insulator. This, in turn, is surrounded by a metal casing which has a thread that is screwed into the cylinder head and normally has a hexagonal section on the top which fits the spark plug socket and enables the installation and removal of spark plugs with a spark plug spanner.

The main purpose of the construction lies in ensuring that the electrical circuit at high voltage on the spark plug is closed with a spark, which jumps from the middle electrode to the earth electrode.