Three different sizes of spark plug. The leftmost plug and center plug are identical in threading and electrodes and may be used interchangeably; the center plug is, however, a compact variant, with smaller hex and porcelain portions outside the head, to be used where space is limited. The rightmost plug has a longer threaded portion, to be used in a thicker head.
{{Information| |Description=Three different sizes of spark plug. The leftmost plug and center plug are identical in threading and electrodes and may be used interchangeably; the center plug is, however, a compact variant, with smaller hex and porcelain po