Lawn Mower Spark Plug Size: How To Find The Right Plug

Do you need help finding your lawn mower’s right spark plug size? You’re not alone. Finding the correct spark plug size can be challenging, but it doesn’t have to be. With simple steps, you can find the perfect fit and get your lawn mower running like new again in no time!

This guide will discuss locating and identifying your lawn mower model’s proper spark plug size.

We will also go over some crispy tips and tricks on adequately maintaining and caring for your spark plugs so that they last longer and perform better. So let’s get started.

Are Lawn Mower Spark Plugs Different Than Vehicle Spark Plugs?

Automobile and lawnmower gasoline engines use the spark plug for the same purpose. But it’s important to note that depending on the specific engine, spark plugs may not be interchangeable between automotive and lawn mower applications.

This is because different engines require different spark plug sizes, and other physical differences may also affect compatibility. Let’s have a look.

Thread Size

There is a size variance between the spark plugs used in automobile and lawn mower engines. Most auto engines use a 14-millimeter thread, while many mower engines use a 12- or 10-millimeter thread. Attempting to mate different threads by force can damage the plug, the engine, or both.

Thread Length

The thread length for auto plugs can be 1/2 inch or 3/4 inch long. But many lawn mower engines use a plug with threads only 3/8 inch long. Using the wrong thread length can impair starting or damage the engine.

Gasket Washer Most mower plugs use a metal gasket washer with a cylinder seal, as do many auto plugs. But some General Motors vehicles use a tapered plug that mates with a tapered hole in the cylinder head to seal the cylinder. These plugs wouldn’t fill a lawn mower cylinder and shouldn’t be used.

Are Lawn Mower Spark Plugs A Universal Size?

Different manufacturers produce different kinds of engines, so the size of the spark plug can vary depending on the type and size of the engine. As a result, no universal spark plug size applies to all lawnmowers.

You can use several methods to identify the spark plug size for your specific engine. You can consult the owner’s manual, measure the existing spark plugs or contact the manufacturer directly for assistance.

How Do You Determine Lawn Mower Spark Plug Size?

If you want to determine the correct spark plug size, you can consider the following factors:

Thread Size

The thread size of a spark plug is measured by two distinct dimensions: pitch and diameter. Thread pitch refers to the difference between each thread on the plug, while thread diameter refers to the thickness of the threaded portion of the spark plug. The measurement for the thread size of your spark plug should be printed on each spark plug or found in your mower’s owner’s manual.

Most power spar plug generally comprises 10 millimeters to 14 millimeters thread diameter and a pitch of 1 millimeter to 1.5 millimeters.

Thread Length

The length of a thread, also known as its reach, is connected to its pitch and diameter. Thread length measures the total distance of a spark plug and is essential for proper engine performance. If your lawn mower’s spark plug has an incorrect thread length, it can lead to overheating and oil fouling of the spark plugs.

The thread length of generally in mowers ranges from 3/8 inch to 0.750 inches. If the length is insufficient to reach the engine socket, it may lead to fuel or oil accumulation around the tips.

In contrast, if the thread length is too long, it can cause overheating and damage your mower’s cylinder.

Additionally, the Wrong thread length of the spark plug can also result in the cylinder of your lawnmower needing to be sealed due to ill-fitting components, which would cause your engine to have trouble starting.

Spark Plug Heat Rating

The heat rating of a spark plug indicates its ability to tolerate specific heat levels. The heat rating is measured on a standardized scale, ranging from two to twelve. A spark plug wchis with a six heat rating is suitable for most lawn mower engines, but it’s essential to check your owner’s manual to ensure you’re using the correct heat rating for your specific engine.

If you use a lower heat rating of the spark plug, it will overheat quickly at a lower temperature compared to a higher rate. So make sure you use the correct spark plug with the suitable heat rating to ensure the proper performance of your engine.

Besides this, if you use an incorrect heat rating, your engine may experience pre-ignition or have difficulty operating at any speed. Therefore, using a spark plug with the appropriate heat rating is always essential to ensure your lawn mower is running correctly.

The Spark Plug Gap

As you work on it, check the spark plug gap to determine. This will tell you if the gap between the plug electrodes is set to the correct distance. The gap should be adjusted with a feeler gauge to ensure the plug is not too far apart or too close.

If the gap is too wide, it can cause problems with ignition. If the gap is narrow enough, it could lead to sufficient airflow. Neither of these scenarios is ideal for your mower’s engine, so ensure the gap is set to the proper size according to your engine’s specifications.

Determine the Type of Lawn Mower

Spark plugs for push mowers and riding mowers are slightly different. Push mower spark plugs usually have pitch thread sizes of 1 millimeter to 1.5 millimeters.

Push mower spark plugs typically have a diameter of 10 millimeters to 12 millimeters and a thread length or “reach” of 9 millimeters to 12 millimeters.

Riding mower spark plugs typically have a pitch of 1 millimeter to 1.5 millimeters, a diameter of 12 millimeters to 14 millimeters, and a thread length or reach of 15 millimeters to 19 millimeters.

Thread Measurements Pitch Diameter Reach
Push Mower Spark Plugs 1-1.5mm 10-12mm 9-12mm
Riding Mower Spark Plugs 1-1.5mm 12-14mm 15-19mm

What happens When you use the wrong spark plug type for your mower? 

Using the appropriate spark plug for your lawn mower is essential for consistent and efficient performance. If you accidentally use the wrong spark plug type, it can lead to several consequences.

Difficulty starting the mower

it can lead to difficulty starting the mower, leaving you frustrated and exhausted.

Run roughly or misfire

It can cause the mower to run roughly or misfire, decreasing its lifespan.

Excessive fuel consumption and emissions

Incorrect spark plugs can also lead to excessive fuel consumption and emission due to a lack of power from the engine.

Overheating spark plug

It may also lead to overheating the spark plug, resulting in engine damage or costly repairs.

Other Specifications to be Considered:

Specific spark plugs have a center electrode that operates at a higher average temperature than others. Such spark plugs are known as “hotter” and “colder” ones.

Some spark plugs elongated further into the combustion chamber than others, termed “longer” or “shorter,” respectively. Considering these spark plug features when selecting one for your lawn mower engine is essential, as they can affect its starting and running performance.

The features mentioned impact how the engine starts and operates and should be adjusted accordingly to match its specifications. If you use too hot or too cold of a spark plug, your motor may experience pre-ignition or difficulty running at any speed. If the plug is too long or short, it can also cause damage to both the piston and the plug itself.

Taking care of the basic specifications can go a long way in keeping your lawn mower engine running smoothly and efficiently. Please select the right type and spark plug features that best fits your lawn mower’s specifications, and always check the gap between electrodes before installing them. Doing so will ensure that you get the best performance from your engine! 

Tips and Tricks

Assuming you have obtained all the technical information, the next step is to buy the correct type of spark plug for your lawn mower. Below are some easy tips to keep in mind before doing so:

Read and understand your owner’s manual

Before purchasing a spark plug, it is essential that you read, understand, and follow all instructions given in your owner’s manual.

Check the spark plug gap

Check the spark plug gap to ensure it is set to the correct size as determined by your mower’s engine specifications.

Purchase quality parts

When shopping for a spark plug, purchase quality replacement parts from a reputable dealer.

Get help from an expert

If you are unsure of which spark plug to purchase, feel free to ask for help from an expert or professional in the automotive industry. You can also contact your manufacturer directly for advice.

Other Method

If you need help finding the information in the online owner’s manual, you can contact the manufacturer through their email addresses, phone numbers, or social media.

Tips For Maintaining Your Spark Plugs

Now that you know the correct spark plug size for your lawn mower, here are some tips to help you keep them in good condition:

  • Clean the spark plug periodically with a wire brush or sandpaper.
  • Replace the spark plug every 100 hours of use or if it’s damaged or worn out.
  • Make sure the gap or corroded.
  • Inspect the spark plug regularly for signs of wear or damage.
  • Use a spark plug wrench to remove and install the spark plugs – never use an adjustable wrench.
  • Ensure the spark plug is gapped correctly to the manufacturer’s specifications before reinstalling it.

These tips will help ensure your spark plugs last longer and perform better, saving you time and money in the long run.

Spark Plug Components:

The spark plug comprises several components: the shell, porcelain insulator, electrodes, electrode tips, and ground straps. Knowing what these parts do is essential if you want to understand how the spark plugs work and determine which type you need for your mower.

The Shell: This component acts as a housing for the spark plug and is usually made of metal. It helps protect the other components from dirt, moisture, and mechanical damage.

The Porcelain Insulator: This acts as an insulator between the outside of the shell and the electrode tip. It prevents electrical current from leaking out and keeps dirt particles away from the electrodes.

The Electrodes: These metal wires carry electricity from the spark plug to the engine’s combustion chamber. They can be single or double ground and come in different sizes, depending on your mower’s engine specifications.

The Electrode Tips: These are located at the end of the electrodes and conduct electricity from the spark plug to the combustion chamber. They need to be periodically replaced, as they can become corroded or worn over time.

The Ground Straps: These metal straps connect the different electrode tips to create a continuous electrical path between them.

By understanding the different spark plug components and their functions, you can be sure you purchase the correct type of spark plug for your lawn mower.


Can I use my car spark plug in my mower?

The answer isn’t a simple yes or no when using a car spark plug in a lawnmower. While it’s possible in some cases, there are a few things to consider first. One of the main factors is the thread size, as automobiles and lawnmowers typically have different thread sizes. The thread length and gap are other essential aspects to remember.

If you want to avoid causing damage to your lawnmower or engine, it’s best to consult the manual and use a spark plug that matches the specifications mentioned. Doing so can ensure optimal performance and longevity for your trusty lawnmower.

Why does the spark plug gap have to be right?

The spark plug is a crucial component of your vehicle’s engine. Ensuring the correct gap between its electrode and center conductor is essential to your engine’s proper functioning. When the gap is too small or too large, it can cause issues with starting your car, engine misfires, or reduced fuel economy. 

To ensure that your spark plug gap is correct, it’s essential to consult your vehicle’s owner manual or a reputable mechanic who can help you adjust it if necessary. Remember, checking and adjusting your spark plug gap can save you from costly repairs.

● Can I change the gap on my spark plug myself?

Yes, you can adjust the gap on your spark plug yourself. However, it is recommended that you consult a professional technician or manual to ensure that the gap is set according to your vehicle’s specifications. Incorrectly adjusting the spark plug gap can lead to damage and costly repairs, so use caution when attempting any adjustments yourself.

● How do I know if my spark plug is bad?

If your vehicle’s engine is producing a sputtering sound, calling out, or starting to miss, it may be a sign that one of your spark plugs has gone wrong and needs replacing. Additionally, you can check the condition of your spark plugs by removing them from the engine and inspecting them for any signs of corrosion, wear, or other damage. If you notice any of these issues, it is time to replace your spark plugs.

What should I do if my spark plug becomes fouled?

If your spark plug becomes fouled, the first step is to remove it from the engine and clean it with a wire brush. If the spark plug is still not functioning correctly, it’s time to replace it with a new one. Check the gap of your new spark plug and adjust it according to your vehicle’s manual if necessary.


In conclusion, understanding a spark plug’s different components and functions is key to keeping your vehicle running smoothly. Regularly inspecting and replacing your spark plugs can help avoid issues with starting or misfiring engines. Consult your owner’s manual or a professional mechanic when changing or adjusting your spark plug gap. Doing so will ensure that your vehicle stays in optimal condition and can help save you from costly repairs in the long run

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