What Size is a Spark Plug Socket

A spark plug socket is a tool meant for screwing the plug (tighten or loosen). It comes in various sizes depending on the hex of the spark plug. Hex (hexagon) is the diameter of the central region of the spark plug. The socket serves the purpose of tightening or loosening the plug through that hex. The size varies with the type of application.

What Size is a Spark Plug Socket?

As for what is the size of a spark plug socket, there is no standard universal size. People often mistake to consider the most common sizes i.e., 13/16″ and 5/8″ as the standard size spark plug socket. These sizes are generally used for cars, whereas a ¾” plug socket is a common one for lawnmowers. Hence, you can find frequently used formats, but they vary based on their application depending on the vehicle. 

How to Find the Spark Plug Socket Size?

Finding the right size of the spark plug socket is not a tricky task, but I often see people messing it up. You can use the following steps to find the size of the spark plug socket.

  • First of all, check your car manual to find out the type and model of the plug. This makes it easy to find the size of the socket.
  • Check the spark plug itself for the size of the socket. If it is accessible then, you can use Vernier calipers to measure the hex size. I see people struggling with the Vernier calipers, too; it is okay. Just consult a mechanic nearby. He will guide you on what you have been doing wrong.

I come across questions like what size is a standard spark plug socket? Well, there is no standard size. The size of any spark plug socket depends on the size and type of the vehicle it is used in. Some are the usual size that people mistakenly took as the ‘standard size,’ and some are quite big.

Spark Plug Socket Size Chart

Here is the chart of the most used spark plug socket size in mm and inches and including their applications.

Size in mm

Size in inches







Small Cars and Motorcycles









Some Old Cars

Best Spark Plug Socket Set

Are you looking for a spark plug socket set and can’t make up your mind? I have an excellent recommendation for you, and I am saying this based on personal experience that Powerbuilt 640855 3/8-Inch Drive Spark Plug Socket Set, 5-Piece is the best spark plug socket set in the market. Not only is it reliable, but its versatile design works in almost every situation. With rubber retention, the plug holds its place, and its chrome vanadium made 6-points deep walls work great.

You will find the following sized plug sockets in there:

  • 5/8-Inch
  • 3/4-Inch
  • 13/16-Inch
  • 14mm
  • 18mm

How to Read Spark Plugs for Tuning?

Optimum functionality

A gray or light tan hue shows that the spark plug is operating at its maximum capability. The temperature is ideal, and the engine is excellent too.


  • Dark color or deposits of any kind (wet or dry) can indicate a vacuum leakage. Large plug gap, a decreased compression, or profoundly retarded timing. Waterlogged deposits show poor oil control or a problem with the valve. Also, sometimes an issue with a breached head gasket can cause a problem too.
  • If your spark plug seems glossier and shinier than usual, it indicated overheating as the tip material melt from the heat, forming a coating.
  • Notice any brownish-yellow deposits on the nose of the insulator? It might be ensnaring. In such cases, breakage might also occur due to thermal expansion.
  • Oxidation and corrosion can lead to a more significant gap which is caused majorly by abnormal electrode erosion.

What Causes Spark Plugs to go Bad Fast?

Spark plugs might not be the most sensitive part of the vehicle, but they sure go bad if you show negligence. Here are some problems that I had to deal with in the past, which made spark plugs wear out pretty quickly.


Heating results in expansion. It also results in the melting of the part of the plug, which is quite common. The real problem begins when this insulation tip melts and kind of glazes the whole thing.


Seeing some carbon on your spark plug is quite common, but if the deposits include leaked oil and unusual carbon deposits, there is a chance your spark plug will go wrong anytime.


Spark plugs are quite tough. The only time there is a chance of breakage is when they experience a thermal shock or expansion i.e., sudden heating and cooling.

Oxidation and Corrosion

Electrodes tend to get oxidized, which can result in corrosion. The degree to which your spark plug can go bad depends on how much corrosion has occurred.

What does a Spark Plug Socket Look Like?

Spark plug sockets have a hexagonal upper view (cross-section) and a cylindrical side view. It is like a hollow cylinder with two open ends. The wrench fits up to one end, whereas the spark plug hex fits the other. It comes in a length of around 2 to 3 inches. The diameter is variable (20 mm, 16mm and 14mm) which depends on what it is being used for.

What is the Best Spark Plug Socket for a Lawnmower?

Lawnmowers are heavy vehicles, which are why spark plug sockets for them are different from what is usually used in cars. I have been using Briggs & Stratton Spark Plug Wrench 5402K for my lawnmower for a long time, and it is one of the best spark plug sockets for lawnmowers. Its versatile designs fit most of the engines and ensure optimum performances. I always use and recommend vehicle equipment’s produced by well-known manufacturers for quality assurance.

Spark Plugs for Lawn Mowers Chart/List




Briggs & Stratton Spark Plug

Champion RC12YC Spark Plug

Maxpower 334058 Spark Plug

What does a Spark Plug Misfire Feel Like?

Here are some indications of how a spark plug misfire would feel. Never neglect them to save your precious time.

Power Loss

A car that shows reluctance in delivering power is a sign the spark plug must have misfired. It feels like jerking, and the vehicle would not accelerate properly. It stops running on all the cylinders.


The sound of the engine changes up to a great extent, which is mostly because all the cylinders are not functional. If you are wondering what does a misfire sounds like? It is sharp sneezing or cracking sound, which is quite distinctive.


The inside of the car starts to smell of oil, which is due to due to the cylinder walls leakage.

Excessive Smoke

I remember when this happened to me, there was too much smoke coming out of the exhaust, which was way more than usual. It is quite easily noticeable.

Are All Spark Plugs the Same Size?

There is no universal size of spark plugs. They come in different sizes and shapes, depending on the vehicle. The size varies depending on the application of the spark plug.

Does Spark Plug Wire Length Matter?

If you ask me about the importance of the length of a spark plug, I can say that it holds great importance, scientifically. The longer the length is, the higher the resistance faced by the electrons would be. This means the voltage would also below. However, particles travel approximately at the speed of light (1ft in 1 nanosecond i.e., 0.000000001 sec) so any addition or deduction would barely make any sense. However, extra-long wires can be a problem; it can be hazardous as excess wire length might end up touch other parts, causing burning due to the engine’s friction. Hence, avoid leaving long wires under the hood.