What Do the Letters on Spark Plugs Mean?
2 Answers
B stands for semiconductor type, C indicates a nickel-copper alloy center electrode, G denotes precious metal electrode, J represents multi-electrode type, R signifies resistor type, T means insulator projected type, and V stands for V-groove spark plug. Composition of a Spark Plug: A spark plug mainly consists of a terminal nut, insulator, terminal stud, center electrode, side electrode, and metal shell. Types of Spark Plugs: Main types of spark plugs include: standard spark plugs, projected insulator spark plugs, electrode-type spark plugs, seat-type spark plugs, multi-electrode spark plugs, and surface-gap spark plugs. Working Principle of Spark Plugs: Under high voltage, the air between the center electrode and side electrode rapidly ionizes, forming positively charged ions and negatively charged free electrons. When the voltage reaches a certain threshold, the number of ions and electrons increases avalanche-like, causing the air to lose insulation properties and forming a discharge channel - this is called "breakdown." At this moment, the gas becomes luminous ("spark") while producing audible "crack" sounds from thermal expansion. These electrical sparks can reach 2000-3000°C, sufficient to ignite the air-fuel mixture in the combustion chamber.
The letters on spark plugs usually refer to the heat range code, something I figured out while working on cars. For example, letters like B or C on NGK spark plugs indicate the strength of heat dissipation. Spark plugs with a high heat range dissipate heat slowly, which prevents stalling in high-performance cars but can lead to carbon buildup during short trips. Those with a low heat range dissipate heat quickly, making them suitable for daily driving. Choosing the right one is crucial—otherwise, the engine might not start or fuel consumption could skyrocket. I’ve seen many car owners replace them carelessly, only to end up with frequent breakdowns. The letters may also carry other information, such as material type—copper-core plugs are cheaper than platinum ones but have a shorter lifespan. In short, before inspecting spark plugs, it’s best to check the car manual for the manufacturer’s recommendations. Don’t underestimate these letters—they determine ignition efficiency and engine health. Choosing the wrong one could cost you unnecessary repair expenses.
