ACDelco 61G / 9G Professional Glow Plug, Pack of 1 Designed to give diesel engines the heat they need for cold starts The ACDelco Professional Glow Plugs can function under higher voltages than other glow plugs GN-type regulating coil Self-regulating to control electrical flow from battery as temperatures rise to avoid overheating Full range of reaches  from 21 mm to 40 mm  to meet chamber requirements in a wide variety of applications