What Are Spark Plugs Made Of? [Main Parts]

Some parts of your car are easy to understand, like the radio and how you drive it. But other parts like the spark plug can be confusing to beginners. So, what are spark plugs made of, anyway?

Generally, spark plugs are crucial to your car’s performance. Their main function is to ignite the air and fuel mixture in the combustion chamber by generating a spark of electricity.

The Answer to What Are Spark Plugs Made Of:

Spark plugs are made of a center electrode, insulator, metal casing, or shell, and a side electrode makes up a spark plug.

The center electrode runs the length of the spark plug and carries electricity from the ignition cable attached to one end to the electrode gap on the other.

Additionally, the insulator is a ceramic case covering most of the central electrode, exposing the upper and lower portions.

The hexagon-shaped metal casing or shell has threads that allow the spark plug to be placed into a tapped socket in the engine cylinder head. Meanwhile, the side electrode is a nickel wire that is short and thick.

In this article, you will know more about the parts of a spark plug and its manufacturing process. So, continue reading to learn more.

Parts of a Spark Plug

Spark plugs are no longer simply plugs and wires. They are under constant pressure to perform within an increasingly rigorous set of parameters, from precise flashover to tight heat ranges.

That performance is made possible by advanced technologies and superior materials. Below are the main parts of spark plugs and their functions.


The insulator, made up of porcelain or aluminum oxide ceramic, gives the spark plug its name. Before using the spark plug, it must be insulated from the engine so that electrical current travels through the electrodes and across the gap.

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It is responsible for keeping the voltage inside the spark plug and preventing it from traveling to other engine parts. It must be made of materials with high dielectric strength.

Metal body

Spark plugs are required for a vehicle to function, as they ignite and power your engine. They are made up of a metal case. The metal case of the spark plug has several features.

It bears the torque of tightening the plug and serves to remove heat from the insulator, passing it onto the cylinder head. Also, it acts as a ground for the sparks passing through the center and side electrodes.

Insulator tip

The insulator tip uses the surface displacement effect to improve the electrical insulation of the spark plug. Thus, it can promote the spark discharge voltage.

Generally, this uses alumina ceramics, advanced manufacturing technology, excellent electrical insulation, and chemical stability.

Its main function is to ensure that voltage is properly sent in the combustion chamber and then reaches the ground once it ignites the fuel.


The spark plug terminal is connected to a high-tension cord through which the high-voltage current from the ignition system flows.

Using this terminal, you can connect standard types of high-tension cords or remove the terminal for vehicles not requiring one.

Central Electrode

Spark plugs contain a central electrode. It lowers the spark voltage and is responsible for securing a reliable spark, improving ignition performance, and reducing the quenching effect.

Its properties include high strength and high resistance to temperature. The tip of the central electrode is usually made with a combination of copper, chromium, or nickel-iron materials.

Ground Electrode

Usually made of nickel-based alloys or iridium reinforcement, the ground electrode is a curved shape conductor responsible for connecting the spark plugs to the ground. Ground electrodes also help in improving ignition performance.

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The threads are the ones screwed into the cylinder head of the spark plugs. A spark plug’s thread comprises 3 dimensions: reach, diameter, and pitch. The silver finish on the threads helps provide resistance to chemicals and moisture.

Electrode Gap

The electrode gap is the distance between the center electrode and the ground electrode. An incorrect electrode gap may decrease engine performance, as the spark magnitude may be too strong or insufficient to ensure complete combustion of the air-fuel mixture.

Proper electrode gap results give the spark plug the ability to produce a more efficient, powerful, and reliable spark.

Manufacturing Process

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A spark plug ignites the air-petrol mixture inside the cylinder. It is placed into the cylinder head and is typically intended to resist 35 kg/cm2 of pressure. Normally, a spark plug can function between 10,000 and 30,000 volts. 

It would be best to use a better quality spark plug-in automobile engineering to resist high pressure and voltage. Throughout the manufacturing and assembly processes, inspections and measurements are performed thoroughly.

A random sampling of spark plugs is pressure tested during the assembly to ensure that the center electrode is sealed properly inside the insulator. Visual inspections ensure that the assembly is done correctly.

Frequently Asked Questions (FAQs):

How much does a spark plug weigh?

Spark plugs serve as a window for the engine and are a valuable tool. A typical spark plug weighs about 10.7 grams. Spark plugs give excellent output regardless of their weight and tiny size.

What are the different sizes of spark plugs?

Spark plug sockets come in 2 sizes: 5/8 inches and 13/16 inches. There are currently 3 thread diameter and pitch sizes for spark plugs. The sizes are 10 mm x 1.0, 12 mm x 1.25, and 14 mm x 1.25.

There are 2 lengths used for the thread reach: 1/2 inch and 3/4 inch. Remember to always use the correct spark plug for the reach.

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What is the white part of a spark plug?

The white part in the spark plug is a ceramic insulator. It is a non-conductive insulator used to seal spark plugs from compression loss.

Ceramic insulators are used in insulating materials that are electrically conductive or temperature-controlled enclosures. It also offers better durability and protection from heat buildup. 

Why is ceramic used in spark plugs?

Ceramics are used in spark plugs because they are known for their excellent insulating capacity. It also retains heat and prevents electrode wear while protecting the spark plug’s assembly from contamination.

The ceramic creates an air gap between the metals used to make spark plugs, increasing the wear resistance of spark plugs.

Are there different spark plug thread sizes?

Yes, there are different spark plug thread sizes. There are currently 3 thread diameter and pitch sizes for spark plugs. The sizes are 10 mm x 1.0, 12 mm x 1.25, and 14 mm x 1.25.

Generally, the first number represents the diameter, and the second number is the pitch.

What are the qualifying criteria for a good spark plug?

A spark plug is designed to produce the electric spark that ignites the compressed air-fuel mixture inside an engine cylinder.

The spark must happen at the correct moment during the combustion cycle. Otherwise, engine power will be decreased or even worse, and the engine might not run properly.

A good spark plug must meet the following requirements:

  1. Spark plugs must be reliable even at high voltages for a long time.
  2. A good spark plug should function under all working conditions of temperature and pressure.
  3. A spark plug must be resistant to corrosion.
  4. Must maintain A proper gap between two electrodes at all times.
  5. The spark plug must have reduced interference to television from the ignition system.
  6. The seals of a spark plug must withstand high pressure and temperature in the combustion chamber during the power strokes.
  7. A spark plug must resist vibration, extreme pressures, temperatures, and disruptive combustion forces. Any failure of the plug will result in the engine misfiring.
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Why is there a gap between the ground and central electrodes?

The gap between the electrodes has an important role. If there is no gap, there is no spark. Creating a spark is key to a car’s ignition system at the right time.

The spark has to be created and timed so that when the mixture of fuel and air enters the cylinder, it gets incinerated by the spark plug’s high voltage electrical pulse.

As a general rule, the wider the air gap, it will create the bigger spark and better combustion. The gap allows the air to flow through the electric arcs.

Also, the width of the gap must be correct. The gap between the spark plug electrodes needs to be set correctly, or the spark plugs won’t fire properly.

What is spark plug ceramic made of?

Ceramics used for spark plugs are made up primarily of alumina. Alumina is a very hard ceramic material that offers high-temperature resistance, making it perfect for hot metal handling and drying equipment applications.

It is lightweight and tough with a high melting point and low thermal expansion rate. Also, it is highly resistant to corrosion, chemical attack, and thermal shock, making alumina a perfect material for forging tools.

How do you maintain a spark plug?  

Spark plugs are a critical component of nearly all combustion engines. It is a very simple device that can endure severe temperature fluxes, extreme pressures, electrical degradation, and chemical attack from the components blended into the gasoline.

Despite this extremely hostile environment, the spark plug can have a very long life if installed properly.

Listed below are five simple tips to properly maintain a spark plug.

  • Inspect new plugs for damages or cracks
  • Clean old spark plugs before removing them
  • Spray the cavity on the center electrode to remove any dust or debris
  • Coat the spark plug thread with an anti-seize compound to prevent galling
  • Coat it with a dielectric compound to deter corrosion and prevent wires from breaking
How often should you change your spark plugs

Is a spark plug gap better, tighter, or wider?

Spark plug gaps should be wide enough to convert the oxygen on the plug’s firing end into an arc. A discharge or spark occurs hot enough to burn up carbon deposits when this happens.

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However, if the gap is too wide, there is a lower chance of this happening, thus less chance of burning off carbon.

Generally, spark plugs with loose gaps can fail prematurely due to the gap widening and increasing misfire. Otherwise, if the gap is too tight, spark plugs are more likely to become fouled from insufficient fuel and air.

Spark Plugs: How’s It Made

Now that you have learned what are spark plugs made of, it is important not to take advantage of them. Spark plugs are designed and engineered to operate over a much wider heat range than ordinary plugs. They resist carbon buildup.

More importantly, they provide better fuel efficiency and lower emissions, improving performance and longer life with optimum combustion.

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