To ensure that you get the correct glow plug, it is best to check the size and shape of the one currently installed so you can compare with the listed plugs. Some important information for selecting the correct glow plug is the type of needed (metal/ ceramic), fitting depth, length and thread size, voltage (V), resistance (Ohm), overall current (A), port type, climate condition, transmission type and date limitation of the unit. As car manufacturers regularly update certain peripherals and design of their models, some glow plugs will only be suitable for particular models of certain years.