Spark plugs with multiple earth electrodes

NGK spark plugs with multiple earth electrodes offer a longer service life with reduced wear.
4-earth-electrode spark plug from NGK

One strategy for extending the service life of a standard spark plug is to equip it with multiple earth electrodes.

With such spark plugs the spark continually jumps over to a different earth electrode. In doing so, the wear is distributed to up to four earth electrodes and the service life is extended.