Spark Plug Anatomy

This post goes out to every customer who has ever opened up that tiny box and said “huh, so that’s what a spark plug looks like.”

There are no major components to a spark plug, as it’s a fairly simple design. First is the terminal at the top of the plug. This is where the boot of the spark plug wire – or ignition coil, depending on your ignition set up – attaches to the spark plug. This is the part of the plug which conducts electricity. That electrical current is carried through the core (or center electrode) of the spark plug.

You’ll note a gap between the spark plug core and the ground electrode. That is where the spark occurs. Electricity jumps from electrode to electrode and causes combustion when mixed with fuel.

Electricity which does not participate in a spark travels through the ground electrode to the ceramic insulator. This allows the current to ground out, completing the circuit.

The only other feature is the hex nut, which takes either a deep socket or specialty spark plug socket – sizes vary by engine.