If you know anything about cars at all, you would’ve heard of spark plugs. What size is a spark plug socket?

Spark plugs affect the whole engine when they fail, so they have to be replaced if you want your car to start up again. Knowing the right size of your spark plug socket is important if you want to get a spark plug that’ll actually work.

Spark plugs come in different sizes. While there’s no standard size, most spark plugs will be either 5/8 inches or 13/16 inches. Specialized engines may also have other sizes. As such, the size of the spark plug sockets will be made to accommodate one of these sizes.

If you need to buy a spark plug socket, you need to keep certain things in mind so you don’t end up with one of the wrong size.

In our research, we considered the various types of spark plugs used and what you need to look out for when buying one.

What Size is a Spark Plug Socket?



What is a Spark Plug Socket?

A spark plug socket is similar to a socket wrench, but made specifically for spark plugs. Since spark plugs have very delicate tips, they need to be handled carefully. Spark plug sockets come with a rubber tip inside to make sure that some of the more vital components of the plug don’t get damaged.

In some cases, they also have a magnet inside which keeps the plug held in place. This is to make sure it doesn’t fall out of the socket, which could again, result in damage.

Spark plug sockets will usually look like a cylinder from the side, but a hexagonal cross-section. It has two open ends – you can fit a wrench on one end to maximize the torque, while the other end will fit the spark plug hex.

When we talk about ‘size’ we are talking about the diameter of the socket.

What Size is a Spark Plug Socket?

Some people have the misconception that spark plugs are all the same size – and therefore the socket is too. After all, the plug just needs to create that initial ignition spark, right? But the size of the spark plug depends greatly on the type of vehicle, so knowing the size is important if you want to get the right spark plug socket.

Most often, the spark plug will be either a 5/8 inch or 13/16 inch one. Most newer vehicles will have a 5/8-inch spark plug. Smaller engines, such as those in lawnmowers will also have a spark plug of this size.As such, the spark plug socket used is also a 5/8-inch one.

13/16-inch sockets are also common, most often found in engines for older vehicles. There are also some other sizes available for more specialized engines. For example, European or Asian brands will sometimes use 14mm plugs, and some Ford models will use 9/16-inch plugs. Motorcycles will sometimes use 3/4-inch plugs. Some lawnmowers and tractors will also use 3/4-inch plugs.

Depending on the kind of vehicle, or the type of engine, the size of the spark plug socket you need will change.

Consider this table for the size of most spark plugs sockets:

Millimeters Inches Type of Vehicle
14 9/16 Some cars, but not very common
16 5/8 Small cars, newer cars and motorcycles
19 3/4 Lawnmowers, tractors and some motorcycles
20 13/16 Older cars
8 11/16 Some old cars

How to Find the Right Size of Your Spark Plug Socket?

Finding the size of the socket is actually not that hard. In fact, all you have to do is find the size of the plug, and you’d know what size socket you need.

To check, all you have to do is look over your car manual to find out what model and type of plug is being used. This will usually give you the size as well, but if it’s not stated there, you can easily look it up once you know what type of plug it is.

You can also use Vernier calipers to measure the hex size of the plug itself. Since there’s no ‘standard’ size, you need to make sure you’ve checked for size correctly before buying a socket for the plug.

Things to Keep In Mind When Buying a Spark Plug Socket

If you’re going to buy a spark plug socket, you need to keep some things in mind and know what exactly you’re looking for. Most spark plug sizes will be covered by some kits, so if you buy the kit itself, you’re pretty much good to go for most sizes of plugs. But if you want to save money and just get what you need, you’ll have to consider the following:

The Type of Engine

As mentioned earlier, the type of engine will also affect the size of the spark plug. The first thing to consider is what type of engine you’re working with. Most cars will have either a 5/8-inch or 13/16-inch plug, but for smaller engines, the plug may be a different size.

Knowing what engine you have can narrow your options down by a lot. You can also do a quick search to find out what plug is used in the engine you have to save time, or simply look over your vehicle’s manual.

Standard or Deep

Sockets don’t just have varying sizes; they can also be used for different kinds of plugs. Look at the plug when it’s sitting in the engine. Is it a bit recessed, or does it look like it’s easily accessible? Some plugs need a deep socket to reach, and these are the ones that are usually recessed. All this means is that your spark plug socket will be a bit longer to reach the plug easier. Most sockets will be around 2 or 3 inches in length, but deep sockets can be a bit longer.

The size of the socket in terms of its diameter doesn’t change depending on whether it is a deep socket or not.


Another factor to keep in mind is the thickness around the plug. How much room is there for you to stick your socket in? If the plug is sitting very close to the walls, then you might need a thin-walled socket to enter. If there is room, you can use one with thicker walls.

Like sizes, the sockets also have varying lengths and thicknesses to reach the plugs. Knowing what type of plug it is, how deep in it sits and how much room there is around it will help you minimize difficulty when you buy your socket.


Charles Redding

Charles Redding

I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.

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