Are all spark plugs 14mm?
No. Spark plugs come in several thread diameters. While 14mm is the standard for many modern passenger cars, engines in motorcycles, lawn equipment, and some older vehicles use 10mm, 12mm, or 18mm threads. This article explains the sizes and how to identify the correct one for your engine.
Common thread sizes used in spark plugs
Spark plugs are manufactured with a few key thread diameters. The following sizes cover most consumer vehicles and equipment; the right size depends on engine design, age, and application.
- 14 mm is by far the most common diameter for modern gasoline engines. Many plugs use M14 threads, typically with a pitch around 1.25 mm (some engines use 1.5 mm). The seat can be gasket-type or washer-type, and reach varies by engine.
- 12 mm plugs appear in a range of motorcycles, ATVs, small cars, and some lawn equipment. They’re common when compact form factors are required or on certain manufacturer designs.
- 18 mm plugs are less common today, but still found on some older or specialized engines, including certain European manufacturers and large-displacement applications.
- 10 mm plugs are used on very small engines such as some chainsaws, string trimmers, and tiny motorcycles; these sizes are far less common in cars but still widely used in outdoor power equipment.
Choosing the correct size is essential for proper sealing, heat transfer, and ignition performance. If you install a plug with the wrong diameter, it can cross-thread, leak compression, or fail to seal properly.
Other plug features to consider
Beyond diameter, spark plugs differ in reach (thread length) and seat type, plus heat range and electrode design. Matching all specs to the engine is important for reliable ignition.
How to identify the correct size for your engine
To find the right spark plug size, start with the vehicle manual or the engine's existing plug. When shopping for replacements, you’ll need to know the thread diameter, thread pitch, reach, and seat type in addition to heat range. Use the steps below:
- Check the owner's manual or manufacturer specifications for the recommended spark plug size and reach.
- Inspect the existing spark plug and measure its thread diameter with calipers, or note the part number and cross-reference with the manufacturer catalog.
- Consider the engine’s age, model, and market region; older engines more often require non-14mm sizes.
- Bring the old plug or packaging to an auto parts store to confirm an exact match; many stores can verify fit against your vehicle VIN if needed.
- Verify compatibility for heat range, electrode design, and seating type in addition to the diameter and reach.
By confirming these specs before purchase, you reduce the risk of damage from cross-threading or poor ignition performance.
Summary
The quick verdict is that spark plugs are not all 14mm in diameter. While 14mm is the standard for most modern cars, you will encounter 10mm, 12mm, and 18mm sizes in smaller machines, older vehicles, and specialized applications. Always verify the exact size and other specs from your manual or the existing plug to ensure a proper, safe replacement.
Can I use 9 16 instead of 14mm for spark plugs?
For the majority of plugs, you need a 5/8” or 16mm socket. Some Fords use 9/16″ plugs, some newer European and Asian vehicles use 14mm plugs, and there are a few applications that use 7/8″, 13/16″, ¾” or 18mm plugs. All spark plugs are 6 sided, except some BMW engines.
What cars use 14mm spark plugs?
- This 12 point 14mm spark plug socket is compatible with 2007+ BMW 3.0L turbocharged engines such as the N54, N55, N20, N26, S55, N63, B46, B48, and B58.
- Along with certain BMW engines, our thin wall spark plug socket is compatible with a variety of MINI vehicles such as the R55, R56, R57, and R60.
What size is a regular spark plug?
There is no single "standard" spark plug size, as they vary by vehicle, but the most common metric hex sizes are 14mm and 16mm (5/8 inch). Other common metric thread sizes include M14 x 1.25 and M18 x 1.5, with different thread sizes being used for different engines. Always check your vehicle's owner's manual or the spark plug itself to determine the correct size.
Common spark plug sizes
- Hex size:
- 14mm: Common in many newer European and Asian vehicles, as well as some Ford vehicles.
- 16mm (5/8 inch): Very common in newer vehicles, small engines, and motorcycles.
- 18mm (13/16 inch): Found in older, large-engine vehicles.
- Thread size:
- M14 x 1.25: A very common thread size, often used with a 13/16" (20.6mm) socket.
- M18 x 1.5: Found on some larger engines.
- M12 x 1.25: Another common metric thread size.
- M10 x 1.0: Generally reserved for smaller engines.
How to find the correct size
- Check the owner's manual: This is the most reliable method.
- Look at the old plug: The size is often printed on the spark plug itself.
- Use an online lookup tool: Enter your vehicle's make, model, and year.
- Ask an auto parts store: An associate can help you find the right plug for your vehicle.
Are spark plugs 14mm?
Spark plugs are responsible for igniting the fuel in the engine cylinders, producing the power needed to run your vehicle. One crucial factor to consider when selecting spark plugs is the thread size. One of the most commonly used thread sizes in automotive engines is 14mm.
