Used to clean-up dirty or damaged spark plug threads
5/8in. hexagon with O-ring female
3/8in. square drive
Consists of a special 12mm spark plug thread with a lead in (for proper alignment) and flutes (for dirt and chip relief)
Also features a 5/8in. hexagon with O-ring and female 3/8in. square drive; requires the use of a 5/8in. spark plug socket, or the female square requires the use of a male 3/8in. square drive