Abstract: A glow plug having a heat range indicated by a colored insulating ring. The insulating ring, along with first and second washers, insulates a central electrode from a glow plug body. Electrical insulation is provided by anodizing the insulating ring. A colored anodizing is used on the insulating ring which is visible from the top of the glow plug, which colored anodizing is indicative of the heat range of the glow plug.