What size spark plug wrench for Honda?
There isn’t a single universal size for Honda spark plug wrenches. Most Honda small engines use a 5/8 inch (16 mm) hex spark plug wrench, though some models require a larger 13/16 inch (21 mm) hex. Check the plug head or the owner’s manual to confirm for your specific model.
In practice, the exact size depends on the hex head of the spark plug installed in your engine, not the thread size. Honda’s light-duty families such as the GX, GCV, and GC lineups typically use plugs with a 5/8" hex, while certain larger or older configurations may employ a 13/16" hex head. Always verify by inspecting the plug itself or consulting the service documentation for your model.
Common hex sizes you may encounter on Honda engines
These two sizes cover the overwhelming majority of spark plugs found in Honda-powered equipment used by homeowners and professionals alike.
- 5/8 inch (16 mm) hex: The standard size for most Honda small engines; corresponds to many 14 mm-thread plugs. Use a 5/8" spark plug socket, typically with a 3/8" drive.
- 13/16 inch (21 mm) hex: Used on a subset of Honda engines with larger or higher-performance plugs. If the 5/8" socket doesn’t fit snugly, try this size.
Note that some compact or older Honda equipment may require other hex sizes; the best approach is to read the plug head or consult the service manual for your exact model.
How to determine the correct size for your exact model
Use these steps to confirm the right wrench size for your Honda engine.
- Inspect the spark plug head: measure the across-flats width to identify the hex size (common values are 5/8" or 13/16").
- Check the engine’s manual, parts diagram, or the plug packaging for the recommended wrench size.
- If you can’t read the plug, start with the 5/8" socket; if it doesn’t seat or feels sloppy, try the 13/16" socket. Do not force the plug or socket.
- After choosing the correct size, torque the plug per the manual (typical range for Honda small engines is roughly 11–20 N·m or 9–15 ft-lb, depending on the plug type).
Reading the plug head and model references
Most spark plugs have the hex size stamped on the plug head. If the stamp is hard to read, refer to the engine’s model and serial number in the owner’s manual or a parts diagram; these documents usually list the correct plug size and wrench requirement.
Having the right size saves time and protects the engine from cross-threading or damage when replacing plugs. Always use a proper spark plug socket with a rubber insert to hold the plug securely and avoid dropping it, especially in tight spaces.
Special considerations for Honda engines
Honda engines cover a wide range of equipment—from lawn mowers and generators to more industrial power units. Because the spark plug size can vary by family and year, always verify against the specific model’s maintenance guide. If in doubt, consult a Honda dealer or certified technician with the engine’s model and serial number. Following the manufacturer’s torque specifications helps ensure a proper seal and reliable starting performance.
Summary
The most common spark plug wrench size for Honda small engines is 5/8" (16 mm). Some models require a larger 13/16" (21 mm) hex. To be sure, inspect the spark plug head, consult the owner’s manual or service diagram for your exact model, and torque the plug according to the official specification. If in doubt, start with 5/8" and move up only if necessary, and always verify the correct size before installation.
