Spark Plug Parts, Types, and Functions Explained

Technically, spark plugs are essential in gasoline internal combustion engines. Without them, your vehicle combustion process will not take place. They transmit electric flow from the ignition system to the combustion chamber to ignite the air-fuel mixture.

The ignition in the combustion cycle causes explosions that force the crankshaft and the flywheel to rotate. So, functioning spark plugs must be in place for any explosion to occur. The spark plugs are small and so most people forget how important they are. But, they must know that, this small component consists of several parts.

Here, we’ll describe spark plug parts and explain the types of spark plugs. But first, let’s see the spark plug design.

spark plug parts and function

What is the design of a spark plug?

As explained earlier, a spark plug is a sparking device that carries electric flow from the ignition system to the combustion chamber for a sparking process.

It has a ceramic insulator, electrically isolated to a threaded metal shell through a central electrode. The spark plug electrode connects to the output terminal of a spark plug wire or ignition coil through a heavily insulated wire. The threaded metal shell is screwed to the engine block. Hence, serving as ground to the engine.

Types of spark plugs

Having seen spark plug definitions, let’s discuss the types of spark plugs to help you make the best buying decisions.

Copper spark plugs

The copper spark plugs are made with solid copper. In this type, the manufacturers produce the central electrode with a nickel alloy, which features the largest diameter among other types. This implies that it requires more voltage to generate electric flow.

Nickel alloy is a soft material and does not stand the test of time. This means copper spark plugs are less durable than platinum and iridium spark plugs. Also, it is not suitable for cars that need high electric flow.

Iridium spark plugs

Here, the manufacturers build the spark plugs with iridium materials. This spark plug type is stronger and lasts longer than the copper and platinum types. However, excellent performance comes with a premium fee. This means that you’ll spend more on Iridium spark plugs.

Manufacturers produce iridium spark plugs with small central electrodes, enabling them to generate electric flow with less voltage. This explains why many car manufacturers have started recommending Iridium spark plugs for their vehicles.

If you’re already using Iridium spark plugs, do not downgrade to copper or platinum plugs because you’ll experience less performance. Invest in Iridium spark plugs if you need the best performance without minding the price.

Platinum spark plugs

This type looks like copper spark plugs, but the central electrodes have platinum tips. The copper plugs feature nickel alloys on the central electrode tips. As a result of the platinum tips, the platinum plugs can last longer than the copper spark plugs. It also generates more heat, making it burn the air-fuel mixture cleaner.

Double platinum spark plugs

Double platinum spark plugs are recommended for vehicles with waste spark ignition systems. The waste spark system causes spark plugs to fire twice, one in the exhaust stroke and the other in the compression stroke.

The firing in the exhaust stroke gets wasted because there’s no ignition here. The waste spark system is more reliable and beneficial to the environment because it is not affected by weather conditions.

To understand the component better, let’s look at spark plug parts and functions.

Spark plug parts name and functions

Here are the various spark plug part and their functions you should know.


As the name implies, this part insulates the center-shafts, the terminals, and the center electrode from the housing. The insulator prevents high voltage from escaping from the electrodes.

The spark plug insulator should be manufactured with materials that exceed the melting point of steel. As a result, the insulator is molded from aluminum oxide ceramics and materials with thermal conductivity, excellent insulation, and mechanical strength at high temperatures.


The terminal is the part you plug in the ignition coil or spark plug wire. This part is attached to a high-tension cord that draws electric flow from the car’s ignition system. On some spark plugs, the terminal has a nut that enables the spark plugs to fit in any vehicle ignition coil or spark plug wires.


The gasket maintains airtightness and makes the combustion chambers and the spark fit each other. However, you must follow the right tightening process and torque the spark plugs properly.

Center shaft

The center shaft, also known as the stem, connects the center electrode with the terminal. The stem is produced from steel material and significantly prevents current loss when traveling from the terminal to the center electrode.

Glass seal

The glass seal ensures airtightness, and it’s located between the insulator and the center shaft. They are produced from mixtures of copper powder and glass powder.


This part is the hexagon area in the spark plug that grips the socket wrench or spark plug spanner for losing and tightening the plugs. The hex has uniform sizes in the automotive industry. It is usually 17 or 14mm.

Center electrode

The function of the center electrode is to lower spark voltage, reduce quenching effects, secure reliable sparks, and improve performance. The center electrode has low resistance, high strength, and high-temperature resistance.

U-groove ground electrode

This is the surface that contacts the air-fuel mixture in the combustion chamber. The U-groove ground is an essential part of the spark plug as it allows the plug to offer large ignition power.

Tapered ground electrode

This is the finely tapered shape on the electrode tip. Its sole purpose is to reduce quenching effects, which enhance ignition.

With spark plug parts explained, let’s see how spark plugs work in gasoline-powered internal combustion engines.

spark plug diagram

How do spark plugs work on engines?

The purpose of the spark plug is to ignite the air-fuel mixture and cause explosions in the combustion chamber. However, it’s important to note that the combustion process does not start with the spark plugs. It starts from the fuel tank.

Technically, the gas pump transports fuel from the tank to the fuel injectors. As the fuel gets to the throttle body, the intake manifold sucks air into the system. The system mixes the air and fuel, forming a highly combustible gas and injected into the cylinders.

As the air-fuel mixture enters the combustion chambers, the ignition coils or distributor high-tension leads send the required voltage to the spark plugs. The pistons compress the air-fuel mixture, making it more combustible. Then, the spark plugs ignite the air-fuel mixture, creating explosions that drive the engine crankshaft.

All these happen swiftly. For instance, internal combustion engines create thousands of explosions per minute.


Q: What is the top of a spark plug called?

The top of the spark plug is called the terminal. This part is the area that has direct contact with the high-voltage current from the ignition system. The ignition coil or distributor leads transmits electric flow to the terminal, which sends it to the center electrode. Most spark plug terminals have nuts that support any ignition coil or high-tension leads.

Q: What is the white part of a spark plug called?

The white part of the spark plug is called the ceramic insulator. It is a protective layer that covers most of the center electrode. However, the insulator does not cover the lower and upper areas of the center electrode. And it is close to the hexagon-shaped area.

Q: What is a coil pack?

Simply put, a coil pack is a pack of ignition coils that are electronically controlled by the car computer. For example, ignition coils that are two, three, or four in one are called coil packs. These types of coils start replacing less-efficient distributors in cars in the 1990s.

Final Words

With the spark plug parts, types and functions explained in this article; you now understand that every part of the component is very important. And the spark plugs should be in good condition at all times.

Plus, you now understand that having a good functioning plug is not enough for optimal engine performance. Buying the right spark plug for your engine plays a big role. For instance, iridium is your guy if you need performance spark plugs without minding the price. And if you want to balance your budget and performance, get platinum spark plugs.


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