The quick answer: use a 13/16-inch spark plug socket for most Honda lawn mower spark plugs. Some older or less common models may use a 5/8-inch socket, so it’s best to confirm by inspecting the plug hex or checking the mower’s manual.
Common sizes used on Honda lawn mowers
To know what you’ll need, it helps to know the sizes you’re likely to encounter. The following options cover the majority of Honda small-engine spark plugs found in lawn mowers.
- 13/16 inch (about 21 mm) across the plug flats — the most common size for Honda lawn mower plugs
- 5/8 inch (about 16 mm) across the plug flats — seen on some older or less common models
If you’re unsure which size your mower requires, measure the hex across the plug or check the model’s documentation. Using the correct socket protects the plug and the engine threads.
How to identify the correct size for your specific model
Follow these steps to confirm the exact socket size for your mower’s spark plug:
- Locate the model number on the mower and consult the owner's manual or Honda’s support site for the spark plug specification.
- Carefully remove dirt from around the spark plug area to prevent debris from entering the cylinder.
- Remove the spark plug boot and visually inspect the plug’s hex.
- Measure across the flats of the plug with a ruler or caliper to determine the hex size (commonly 13/16" or 5/8").
- Match the measurement to a spark plug socket: if it’s about 13/16", use a 13/16" socket; if it’s about 5/8", use a 5/8" socket.
Having the correct size socket helps prevent cam-out and damage to the plug’s hex or the cylinder head. If you don’t have calipers, a quick check with a 13/16" socket that fits snugly is a practical test for most Honda engines.
Removal and reinstallation tips
Once you’ve identified the right socket, follow these practical steps to safely remove and reinstall the spark plug:
- Disconnect the spark plug boot by pulling straight up—do not twist the wire.
- Clean the area around the plug to prevent dirt from falling into the engine when you remove the plug.
- Attach the correct spark plug socket to a ratchet, and loosen the plug by turning counterclockwise until it backs out.
- Inspect the plug for wear, fouling, or correct gap. Replace if necessary with the appropriate Honda-approved plug.
- Reinstall the plug by threading it in by hand to avoid cross-threading, then snug gently and finish with a light turn (avoid over-tightening; usually a quarter-turn past snug is sufficient, or follow the manual’s torque guidance).
Using the right socket and proper technique helps ensure a clean seal and reliable starting performance for your mower.
Tips and cautions
Always work on a cool engine and avoid forcing the plug if it resists. If you don’t have the exact socket size, you can temporarily use a slightly larger socket with care, but resist the temptation to force it—this can strip the plug head or damage the cylinder.
Summary
For most Honda lawn mowers, a 13/16-inch spark plug socket is the standard choice. Some models may require a 5/8-inch socket, so verify by checking the plug hex or the mower’s manual. Always clean the area, handle the boot carefully, and torque the plug appropriately to ensure dependable starts and long engine life.