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.