Lawn mower plug spanner. How To Find The Right Spark Plug Socket Size ( 4 FAQs)

Spark Plug Sockets Sizes

Spark plugs are a critical component of a combustion engine that will eventually wear out. While it is technically possible to remove wasted plugs using a standard deep well socket, there is a good possibility you may harm good ones. When working on a car, truck, motorcycle, or lawnmower, you can always use a spark plug socket.

Almost every spark plug is available in a size of HEX sizes. Hex refers to the socket or diameter in the middle of a spark plug used to spin, screw-down, or unscrew the spark plug.

In our guide, you can learn all you need to know about any spark plug size you encounter, from little engines to huge automobiles listed on our spark plug socket size chart, where you can see additional sizes in use.

By the conclusion, you’ll understand spark plug wrench sizes and be able to utilize our simple spark plug sizes chart to determine which size plug should be installed in which type of engine. (Read Is There A Difference Between Star And Torx)

What are the common spark plug socket sizes?

What’s the most common size of spark plug socket? You’ll discover there is no standard size spark plug socket size in your plug socket set. The most common sizes, 13/16′′ and 5/8′′ are sometimes confused with standard spark plug socket sizes.

Although a 3/4” plug socket is common in lawnmowers, these sizes are mainly found in cars. As a result, common formats are available; however, they vary depending on the vehicle.

Finding the proper spark plug socket size is not difficult, but many individuals make a mistake. To find the size of the spark plug socket, follow the procedures below.

  • To begin, check your manual to find the kind and model of the pre-gapped plug. This makes determining the socket size simple.
  • Check the size of the socket on the spark plug itself. If you have access to it, you can measure the hex size with Vernier calipers.

Here you can find the concise spark plug socket size chart that shows most plug sizes in use and answers the vehicles on which they are used. You will notice no direct spark plug socket sizes mm that relate to spark plug socket size metric. (Read Allen Key Sizes In mm) You have both on a different vehicle; you will need to check which your vehicle has or have in your kit, so you won’t forget you have a socket or need to convert mm to metric.

Spark Plug SizeApplication

It is worth noting here you should use a torque wrench with your spark plug when installing the spark plug. A torque wrench tool can stop you from over-tightening the plug and stripping the cylinder head thread.

A socket wrench of this type should fit various sockets, or there will be an adapter so the tool can fit assorted sizes. (Find the Best Complete Socket Set)

What are the 3 spark plug socket sizes?

Only a few deep and regular spark plug sockets are available. Deep sockets function far better when dealing with a recessed plug. Universal joints are articulated joints that allow you to rotate the wrench around one axis while rotating the reliable hexagon sockets along another axis. Spark plug sockets are typically supplied individually but sets with assorted sizes and extensions are also available. 7/8″ sockets are rarely provided in socket sets because of their unique purpose and length and require a 1/2″ drive.

Although there are 12-point versions of several sockets, the 6-point version is significantly more common. Only a few automobiles, such as some newer BMW engines, use 12-point plugs.

Are spark plugs all the same size?

Spark plug sockets are specifically designed to hold spark plugs. They come with two interiors, both of which hold the plug securely without damaging it.

Rubber inset sockets, for example, produce a soft rubber cradle for the plug to sit in, whereas magnetic sockets employ magnets to hold the plug insulator in place.

While this may not seem like much compared to the varied sizes of the deep socket, it can make a significant difference. The unique bed prevents sliding during work, making installation and removal go more quickly.

This can save lots of time and save a few bashed knuckles where spark plugs are situated deep within the engine block, where you may also need an extension on some cars. Employing a spark plug socket reduces the danger of damaging the insulation. (Read Metric To Sae Conversion)

Sizes of Spark Plug Sockets

There are only a few deep and normal spark plug socket set variations available. When dealing with a recessed plug, deep sockets will work better in a complex automotive engine such as a BMW.

Most sockets accept a standard 3/8” drive, and some kits can contain one or more extensions or swivels. Thin walls are preferable because they allow easier access to deep depths.

Is there a special spark plug socket?

There are two sizes of spark plugs: 5/8 inch and 13/16 inch. The rubber insert in most spark plug sockets keeps the plug tightly in place.

Torque wrenches have a gauge that shows how much torque is applied when the wrench is turned. A universal joint may be useful if you can’t fit a wrench and extension in the space surrounding your spark plug.

A set of boot pliers, a clean rag, some rubbing alcohol, a tube of anti-seize, and compressed air or a wet/dry vacuum should all be on hand as well.

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Spark plug sockets are specifically designed to attach to spark plugs without damaging them, unlike standard socket wrenches. Magnetic sockets hold the plug in place via magnets and rubber inset sockets. (Read Light Bulb Base Size Chart)

This means there is a lower chance of damaging the spark plugs insulation in the car’s engine block. Spark plugs have a unique bed that prevents the plug from slipping in the socket. This allows for the installation and maintenance of engine parts to be completed in a shorter time.

This will make an enormous difference to car owners in many cars whose spark plugs are buried deep into the engine block. They are less concerned about damaging any portion of the car, such as stripping threads or dropping the plug because of the spark plug size.

How To Find The Right Spark Plug Socket Size (4 FAQs)

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In this article, we’ll help you find the right spark plug socket size for your car. We’ll also examine the types of spark plug sockets and answer a few related questions.

How To Find The Right Spark Plug Socket Size

A spark plug socket is the right tool for handling spark plugs.

It’s specifically designed to handle an old plug (or new plug in case of replacement) without damaging any spark plug wires or threads.

You can usually invest in socket sets that contain the common size for spark plug sockets as well as other interchangeable sizes (so you always have the correct size at hand).

If not, spark plug sockets are individually available in different size varieties to match the spark plug, the most common size being the 5/8 inch size socket. Another common size is the 13/16 inch size socket.

Here are some typical spark plug socket sizes:

Socket Size(in inches)Socket Size(in mm)Typical Application
5/8 16 In a newer vehicle or small engine cars
13/16 20 Older vehicle engines
9/16 14 Newer Asian cars and Ford vehicle engines
3/4 18 Motorcycles
3/4 19 Lawn mowers and small engine cars
7/8 22 Aviation vehicles and tractors
11/16 18 Motorcycle engines, small engine BMW cars

You’ll need to pick a relevant spark plug socket depending on the size of your spark plug.

Also, keep in mind the thread size of your spark plug threads. Spark plugs are available in two thread size options for motorcycles — 1/2 and 3/4 inches. For other vehicles, spark plug threads are also available in thread sizes like 8, 10, 12, 14, and 18 mm.

So, make sure your new spark plug has similar threads as the old one because if you use the wrong thread size, your engine will be prone to misfires and carbon fouling.

Next, let’s look at the different types of socket sets available in the market.

Types Of Spark Plug Sockets

Spark plug sockets are available in various extensions and interchangeable sizes. But their core component is usually manufactured in two styles.

A. Magnetic Spark Plug Socket

A magnetic spark plug socket consists of a small magnet inside a thin wall of the deep socket.

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This magnet will attach to the spark plug tip and prevent it from falling off whenever you remove a spark plug. This way, you don’t misplace your spark plugs during the process of removing them from your engine.

B. Rubber Grommet Spark Plug Socket

As the name suggests, a rubber grommet socket contains a rubber insert in the deep end of the spark plug socket.

This is to secure the spark plug tip in place when removing an old plug. It prevents any bends or scratches and keeps the plug tips safe.

Now that we’ve gotten the basics on spark plug socket sizes and types, let’s look at some other related queries on spark plugs, and their answers.

Spark Plug FAQs

Here’s what you should know about spark plug sockets:

What Is A Spark Plug Socket?

A spark plug socket is very similar to a standard socket, except that it may also have a swivel extension bar to reach the spark plug hole without damaging other wires.

Like most other sockets, these are available in interchangeable sizes and can be attached to a torque wrench for better torque. However, spark plug sockets can handle more delicate repairs without damaging the equipment they’re working with.

Some spark plugs are equipped with a magnet or a rubber grommet inside the socket.

How Does A Spark Plug Socket Work?

Spark plug sockets have a very similar function to that of a standard deep socket — to tighten or loosen a piece of equipment.

To work, spark plug sockets attach to a turning tool with a square drive socket. They sometimes also have a hex or bi-hex head.

In short, you just fit the spark plug tip inside the socket head and then twist to loosen the spark plugs.

The spark plug socket will work differently depending on the type of socket you’re using — whether it’s magnetic or has a rubber insert.

Do I Need A Special Socket For Spark Plugs?

Yes and no. While a regular socket should do the job well too, a special socket is often the right tool for the job.

Modern car engines have a very complicated spark plug placement. Some spark plugs are placed deep inside the engine, surrounded by spark plug threads and wires.

A regular socket can easily handle a basic spark plug replacement. But you’ll need the right socket size with swivel handles to reach the spark plugs without damaging the wires during changing.

A universal joint socket may also do the job. Plus, a magnetic or rubber insert universal joint socket can better handle a new plug than regular socket sets.

If you’re unsure, it’s best to take professional advice on the tools you should be using for your car.

How To Use A Spark Plug Socket?

Here’s how you can use a universal joint or a regular socket to remove spark plugs:

  • Start by locating your spark plugs. Look for the distributor cap, coil pack, or ignition coil surrounded by plug wires. Trace these wires to the engine block, where it’s attached to spark plug sets.
  • Remove each spark plug wire from the spark plugs. You may want to label your spark plug wires to know which one goes where.
  • Next, take your spark plug socket and fit it on the top of the spark plug. Ensure that it’s the right size. Ideally, it should fit snugly but not move around the plug.
  • Next, attach the socket wrench (or torque wrench, if you’re using one) to the back of the deep socket. You can also add an extension bar between the torque wrench and the socket.
  • All that’s left to do is rotate the wrench using the extension bar, and loosen the spark plug from the spark plug hole.

Note: When installing a new plug, you need to follow the same procedure and add dielectric grease on the spark boot. Dielectric grease prevents the new plug from sticking to the boot. Next, adjust the torque on the socket wrench according to the recommended torque spec, and you should be done!

Final Thoughts

A spark plug replacement is pretty straightforward for DIY repair enthusiasts. However, damaged or incorrectly sized spark plugs can cause problems with the engine that may cascade.

So, using the correct size and type for your spark plugs is very important, just like knowing if your engine uses a coil pack, coil-on-plug, or single ignition coil.

Ideally, you should always err on the side of caution with your car repairs. Incorrect handling of spark plugs can cause misfires and engine failure. If you’re someone who isn’t confident about their mechanical skills, it’s best to leave the job to a mechanic.

RepairSmith is a mobile auto repair and maintenance solution with competitive, upfront pricing and a range of repair solutions. All repairs even come with a 12-month | 12,000 miles warranty.

Fill out this online form for a free cost estimate on your spark plug replacement.

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Mower Won’t Start No Spark (This Is Why)

Pulling and pulling and nothing, a mower without spark, is useless. In this post, we’ll cover all the most common ignition system failures.

Mower won’t start any spark? Common reasons a lawnmower has no spark include:

None of these tests are difficult, and twenty minutes from now, you’ll know why your mower has no spark.This post will have you covered, but if you need video help diagnosing no spark or help to fit a new coil, check out “Mower won’t start video.”

Checking Lawnmower Spark

Since you’ve checked the spark already, I’m guessing you know the procedure. However, it’s worth pointing out, getting this test wrong can lead to misdiagnosing and replacing the ignition coil or other parts unnecessarily.

Spark testing is, as you know, a simple test, you won’t need any special tools here, but a spark testing tool does make the job easier and totally foolproof.

If you need video help, check out the mower “Mower spark test video,” where I cover the whole process.

Tools needed

For these tests, you’ll need a plug spanner, insulated pliers, screwdrivers, and a spark plug is useful. You’ll also need a helper, as we’re not using a spark testing tool. It can be difficult to crank over the engine and, at the same time, check for spark. With all the tools gathered and a helper on hand, we’ll get right to it.

Spark Testing

As we’ll have a helper cranking over the engine, that means the blade will be spinning, and even though the engine’s not running, it can still remove body parts, so, you know!

You must use insulated pliers (plastic/rubber-handled pliers) to hold the plug as the voltages produced are enough to give you a jolt, which isn’t pleasant.

Tools – Plug spanner, insulated pliers, and a spark plug will be needed.

Spark test tools

Step 1 – Remove the spark plug wire by twisting and pulling, then using the plug tool, remove the spark plug.

Step 2 – Reattach the spark plug wire to the plug. Using your insulated pliers, hold the plug threads firmly against the metal of the engine. This is known as grounding. If the plug doesn’t make good contact with the metal of the engine, you won’t get a spark.

Easy Way to Remove a Spark Plug without Spark Plug Socket

Step 3 – While you watch for spark, have the helper hold the bail lever as normal and yank on the pull cord.

If you have no spark, swap out the plug and test again.

If you still have no spark, it is most likely a failed coil, but best to check the on/off switch assembly first.

Common Spark Plug Faults

A healthy spark plug is essential for reliability, power, and smooth running. Plugs have a tough job. They carry high voltages and live at the heart of the engine where it’s hottest.

Making matters worse for the plug is its location – right out front of the engine. So getting shoved into fences and trees is all part of a spark plug’s life, and you thought you had it hard!These are the most common spark plug faults:

Lawn Mower Spark Plug Wrench Size

  • Wrong plug type
  • Dirty plug
  • Bad plug gap
  • Cracked spark plug insulator

Wrong Plug Type

Plugs areas you know are graded; each engine will have a particular plug code. So even though a plug fits, it doesn’t mean it’s correct. Plugs are graded by heat. The plug should get hot enough to burn off contaminants but not so hot that it pre-ignites. Wrong plug types can cause all types of problems, from hard starting, rough running, hot start failures, etc.

Plug type – Check your plug type with your mower engine maker.

An incorrect plug type will lead to intermittent problems.

Dirty Plug

Self-explanatory, it’s a plug that’s contaminated by too much gas (flooding), carbon, or oil. All of these will prevent the plug from doing its job. Flooding may be caused for a few reasons – blocked air filter, faulty choke, overuse of choke, tipping mower over on its carburetor side, and carburetor fault. Check out the video “How to fix a flooded engine.”

Carbon build-up in the engine is a normal condition. Fuel type, oil type, maintenance, and plug type all affect how quickly it builds.

Oil on the plug is also common. It’s caused by too much oil, blocked crankcase breather, head gasket fault, engine wear, and wrong plug type. Check out the video “How to clean a plug.”

Bad Plug Gap

A spark plug function is obviously to create a spark, and it can only do this if the electrode gap is correct. The coil has been designed to create a sufficient spark to jump a pre-determined spark plug gap.

  • No gap, means no spark
  • Gap too small means poor running or no start
  • Gap too big means no start and risks damaging the coil

A plug gap tool is used to set the spark plugs gap. The electrode is manipulated to the correct size by simply bending it with pliers. Check out the video “How to gap a plug.”

Plug gap – The gap is important. Too small or too big can lead to no starts or poor running.

Cracked Plug Insulator

Self-explanatory too. The insulator is the white ceramic material of the plug’s body, and as said earlier, plugs are at risk of being damaged by bumping into obstacles. If the insulator breaks or cracks, the plug stops working.

Common Spark Plug Wire Faults

A spark plug wire has a few particular problems that affect them, depending on a few variables, like how and where they’re stored.

The common faults I see again and again include:

Loose Terminal

Caused by our old friends, the trees, shrubs, and fences. The plug wire terminal that clips to the spark plug becomes loose, and that can cause no starts, poor running, and intermittent starting/running.The fix here is simple, squeeze the terminal body using pliers to tighten it.

A loose terminal will cause the engine to misfire or not start at all. The quick fix here is to squeeze the terminal until it fits snugly on the plug.

Faulty Terminal

Because this cap was loose, it created arching, which burnt the metal of the terminal cap.

Faulty terminal connector – It’s different but related to a loose connector. A loose connector will often turn into a faulty one as the spark starts to jump inside the terminal, burning it or setting up conditions for corrosion to take hold.

The outcome is the same, no spark or poor running. A replacement terminal can be purchased and fitted to solve this issue.

Damaged Plug Wire

Plug wire rubbing off the engine cover can cause the insulation to wear and the coil to ground. But more often than not, a damaged plug wire means rodents. Mice love wiring insulation, and unfortunately, our furry friends have cost us a coil.

Sure, you can wrap them with insulation tape, but it’s only a quick fix. The long-term repair is to replace.

Damaged wire – Mice love to chew on the wiring insulation.

Common Stop/StartAssembly Faults

Most mower owners are familiar with the bail lever at the handlebars, which must be held to start the mower. Most mowers will use this type of stop/start system; other manufacturers may incorporate the stop/start function with the throttle lever. But apart from this difference, all other components will be very similar.

The main components of the stop/start assembly include:

  • Bail/throttle lever
  • Cable
  • Flywheel brake assembly
  • Stop/start switch
  • Coil control wire

Bail / Throttle Lever

Common faults here include disconnected, out of adjustment, or broken levers.


The cables break and stretch, so it’s not uncommon for the bail lever to work, but because the cable has stretched, it doesn’t move the brake assembly to the start position.

Stop / start cable

Flywheel Brake Assembly

Common faults here include cable out of adjustment, meaning the bail lever doesn’t pull the brake to the off position.

Flywheel assembly

Stop/Start Switch

This is the on/off switch. It’s fitted at the flywheel brake assembly. When the bail lever pulls the assembly, it pushes on the switch removing the ground connection to the coil. This allows the mower to start.

On /off switch

Coil control – Here’s a different mower coil control switch. It’s a very simple connection; the contact points must separate before the coil and plug will create a spark.

The Coil (also known as Armature)

The control wire is connected from the stop/start switch on the flywheel brake assembly to the coil, which is fitted to the engine. The coil and plug won’t produce a spark so long as the control wire is connected to the ground (Metal of the engine).

A common fault is the chafing of the control wire on the engine (shorting to the ground); this effect is the same as releasing the bail lever – turns the engine off.

Check coil control wire for chafing, especially anywhere the wiring turns sharply around the engine.

Coil control wire – Coil control is a single wire with a push-on connection. Often they’ll come loose, and when they do, the mower won’t turn off.

Common Coil Faults

Coils generally work, or they don’t. Occasionally, you’ll get a coil that works when it’s cold and stops when the engine heats up. Coils are solid-state units – they can’t be repaired. Testing a coil and fitting a new one is easy; I wrote a whole post about it right here “Push mower hard to start when hot”.

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Or check out the video here; it covers spark checking, diagnosing, and replacing the coil. If you need to replace the coil, check out the great deals on the Amazon link below.

Coils – Lawnmower coils give lots of problems; I replace tons of them.

Related Questions

Can a spark plug have a bad spark? Spark plugs wear out. A spark plug should be changed once every year at the start of the new season. You can check the spark plug for spark by removing it, connecting the plug wire, grounding it off the engine, and turning over the engine.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

And the best part. it’s free!

Spark Plug Socket Size Chart | Learn about Spark Plugs, Socket Sizes

If you are one of those people who like to work on your own cars and bikes, then you must be familiar with Spark Plugs. They are a part of the ignition system in an automobile (gasoline or petrol) and are responsible for igniting the mixture of air and fuel in each cylinder. For efficient burning of fuel, the spark plug must in a very good condition. As a part of maintenance (or repairs), you have to remove and clean the spark plugs or replace them if it isn’t firing properly. You have to use a wrench or ratchet with correct socket size to remove and install the spark plug. In this guide, let us get to know a little bit about Spark Plugs, different socket sizes for spark plugs and also how to find the correct spark plug socket size.

Ignition System in Cars

When you insert the key into the car and turn it to ignition (or press the electronic start button in most modern cars), the ECU of the car makes an electrical connection between the battery and the primary ignition coil.

As we crank the engine, the pulsating voltage in the primary coil induces a voltage in the secondary coil, which can be as high 20,000V – 25,000V (or more). This high voltage is then applied to the spark plug, which then creates an arc in the air gap, thus igniting the air – fuel mixture. This causes a high pressure in the cylinder and as a result it pushes the piston down and starting the engine.

Once the engine is running, the ignition system repeats this process of converting low voltage from battery to high voltage, sending it to spark plug and the arc igniting the fuel as directed by the ECU.

A Brief Note on Spark Plugs

It is clear from the above discussion that the ignition system is an important part of all internal combustion engines. While there are many parts in a typical ignition system, let us FOCUS on the Spark Plug.

A Spark Plug consists of a main central electrode surrounded by a ceramic insulator. A portion of this insulator is covered with a metal shell with threads that allow it to be screwed into the cylinder head. There is another electrode, which is the ground electrode. It is part of the metal shell and gets connected to the metal frame of the car (which acts as the negative terminal).

There is a small gap between the central electrode and the ground electrode known as the air gap. When we create a potential difference (by applying the high voltage from the ignition coil to the central electrode) between the two electrodes, the gas molecules in the air gap are ionized and forms a charge region.

This charge region bridges the air gap between the electrodes. With sufficient electrical energy, current flows the charge region and the gas molecules get super-hot and create a plasma (that looks like an arc). This high temperature of the plasma is responsible for igniting the fuel-air mixture.

An important point about the design of the spark plug is that the metal shell not only acts as a ground terminal but also provides the structural strength to bear the torque while tightening or removing the plug from the cylinder.

As a result, the metal shell also consists of the hex nut, just above the threads. We can use a wrench or ratchet with correct socket size to insert or remove the spark plug.

Spark Plug Size

International Organization for Standardization (ISO) and Society of Automotive Engineers (SAE) have respective standards for the length, hex size, thread diameter and pitch of spark plugs.

When we say “spark plug size”, we usually mean the diameter of the threads of the spark plug. The two most common spark plug sizes in modern motorcycles and small cars are 14mm and 18mm.

Some automobile manufacturers also use 16mm high-thread count spark plugs and 12mm long-reach spark plugs.

Spark Plug Socket Size Chart

A Spark Plug Socket Size is dependent on the size of the hex nut on the metal shell. The following table shows the Spark Plug Socket Size Chart for some of the most commonly used spark plugs.

Spark Plug Size (inches)

Removing and Installing Spark Plug

A good spark plug will not only burn fuel efficiently (without any wastage) but also helps the engine in running for a long time. Hence, it is essential to inspect, clean and if necessary, replace spark plugs in your cars and motorbikes. Most automobile user manuals (or service manuals) specify when to inspect/clean/replace spark plugs.

The good thing about spark plugs is that they are relatively simple components to work with and you can remove and install them without the need for going to a work shop. If you plan to take out the spark plug yourself, then it is essential that you have the proper tools and also take necessary precautions.

Speaking of tools, you need a ratchet, a spark plug socket and a universal joint. Here, selecting the right spark plug socket size is very important. In case of a wrong socket, it will slip off the plug and can break the insulator (porcelain).

Once you have the right tools, make sure that the engine is off for a significant period so that it is properly cool. Do not work on recently shut off engines. Remove the spark plug wire first.

Then, using the combination of ratchet, spark plug socket and if necessary, an extension, unscrew the spark plug and while you take out the socket, the spark plug will come with it.

Once the spark plug is out, inspect and clean it. Before installing the spark plug back into the cylinder, use a flash light and see whether the spark plug seat on the cylinder is clean or not.

Now, seat the spark plug and screw it with hand for a couple of turns. Then, you can use the ratchet and socket to tighten the spark plug. If you are complete newbie, then you can use a torque wrench.


Spark plugs are an important part of modern IC engines (gasoline/petrol). A healthy spark plug will help the engine burn fuel more efficiently. So, frequent all automobile manufacturers recommend regular inspection of spark plugs. You can easily remove-inspect-clean-install spark plugs on your own, provided you have the right set of tools. And an important tool is the Spark Plug Socket. In this guide, we saw some popular spark plug socket sizes and also the procedure to remove and install a spark plug.