If you are looking to get a glow plug nut, it would be a good idea to educate yourself on the difference between spark plugs and glow plugs. All combustion engines require 3 things to work, namely air, fuel and heat or an ignition source. Both glow plugs and spark plugs are the ignition source in a combustion engine. The difference is in the type of engine that they are found in. Glow plugs are in diesel engines while spark plugs are only found in gasoline engines.
It is possible to start a warm diesel engine without use of a glow plug, or in warm climates, thanks to the relatively high temperature of the intake air as well as the relatively low ignition temperature of diesel. But this is not enough to ensure proper ignition of the injected fuel in all temperatures, something that results into increased exhaust emissions. Glow plugs are electrical heating devices that solve this issue. They are located in each cylinder of the diesel engine to ensure reliable starts in all forms of weather.
A glow plug is simply a long, thin piece of metal that has a heating element at the tip. This heating element is constructed from materials that resist oxidation as well as high temperatures. Unlike spark plugs that work continuously while the car is being driven, glow plugs are only required during the ignition process. They work by electrifying the heating element so that it can heat up and emit visible light. The intake air is compressed before the fuel injector spray directs the fuel onto the hot tip of the glow plug during the injection of the fuel. After the fuel is injected, it mixes with the compressed air, evaporates and starts combustion almost simultaneously.