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How to Know What Size Spark Plug Your Weed Whacker Requires

By Alice Moon ; Updated September 21, 2017
Look for the identifying marks on the white body of the spark plug.

Weed whacker is a generic term for a yard trimmer or string trimmer. Advice regarding how often to change the spark plug in these devices varies with the manufacturer. Some recommend cleaning, inspecting and replacing the plug every three months, every 90 working hours or earlier, while others suggest a yearly check.

Plugs may look similar but they have important differences in their function. The right plug means you have the proper size, the correct thread reach and the right heat range needed for the trimmer’s motor. This and other important information is encoded within the numbers and letters that make up the design symbols on your spark plug.

Grasp the rubber boot covering the spark plug between your thumb and forefinger. Pull the boot straight off to expose the plug. Use a spark plug socket wrench sized to fit the spark plug to unscrew and remove the plug.

Check the old spark plug. If you have the original plug in your weed whacker or you have replaced the plugs faithfully with the proper plug over time, you will be able to find the code numbers on the body of the plug itself to determine its replacement.

Check your garage for the old spark plug box. The box often contains the same combination of numbers and letters that you need to identify the proper replacement plug.

Check the user’s manual. Your trimmer’s manual may include the ID numbers for the types of plugs that are compatible with your trimmer.

Gather information about your trimmer. You will need the make and model number at the ready to find the correct spark plug information. Check the manufacturer’s website FAQ or Use and Care section for the correct type of plug and the proper plug gap for your make and model. Call or email the company for the information if it is not listed on the website.


Things You Will Need

  • Spark plug socket wrench