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What thread is a Honda spark plug?

When replacing a spark plug on a Honda vehicle or machine, the thread size isn’t universal. Different engines use different thread diameters and pitches. This guide explains the common sizes and how to verify the correct one for your model.

Common thread sizes by Honda product line

Most Honda engines fall into two broad categories: cars and motorcycles/small engines. The thread diameter and pitch you need is typically tied to these categories, with exceptions based on the exact model and generation.

Automotive engines (Honda cars and light trucks): typically 14 mm diameter with a 1.25 mm pitch (14x1.25).

Motorcycles, ATVs, and many small engines: typically 12 mm diameter with a 1.25 mm pitch (12x1.25).

Note that some older or specialty Honda engines may use different thread specifications. Always confirm with the service manual or the OEM parts catalog for your exact model.

How to verify the correct thread size

To identify the proper spark plug thread for your Honda, follow these steps:

Check your vehicle’s or engine’s owner’s manual or service manual for the exact spark plug specification.

Look up the OEM spark plug part number for your engine model; the part catalog will list thread size and reach.

If you’re replacing an existing plug, inspect the old plug’s threads or measure the thread diameter with calipers and verify pitch with a plug gauge.

Consult a Honda dealership or authorized parts retailer if you’re unsure; provide the engine model, year, and VIN if possible.

Getting the thread right matters: the wrong size can cross-thread, damage the cylinder head, or fail to seal properly, leading to compression leaks and poor performance.

Additional considerations when replacing spark plugs

Torque, reach, and heat range

Besides the thread size, you should also select the correct heat range, reach (how far the plug extends into the combustion chamber), and the proper torque. Honda engines have specific torque specs for spark plugs, and using the wrong torque can cause the plug to seize or loosen.

When shopping for replacements, purchasing the exact OEM part or an equivalent recommended by Honda/NGK/Autolite will help ensure compatibility across diameter, pitch, and heat range.

Summary

In short, there isn’t a single thread size that covers all Honda spark plugs. Automotive engines typically use a 14x1.25 thread, while motorcycles and small engines commonly use 12x1.25. Always verify with your manual, part number, or dealer to avoid cross-threading or sealing issues. Proper sizing, along with the correct heat range and torque, ensures reliable starts and engine health.

What thread size is my spark plug?

Common spark plug thread sizes are M14 x 1.25, M18 x 1.5, M12 x 1.25, and M10 x 1.0, where the first number is the diameter in millimeters and the second number is the pitch in millimeters. The most common size for modern vehicles is M14 x 1.25.

Size	Diameter (mm)	Pitch (mm)
M18 x 1.5	18	1.50
M14 x 1.25	14	1.25
M12 x 1.25	12	1.25
M10 x 1.0	10	1.00

M14 x 1.25: The most common size found in many modern cars.
M18 x 1.5: A larger, less common size.
M12 x 1.25: Often used in smaller engines, including some European and Japanese models.
M10 x 1.0: Typically found in smaller engines and some older or specialized applications.

What size is a Honda spark plug socket?

The most common Honda spark plug socket sizes are 14mm for many newer models and 5/8 inch (approximately 16mm) for many older models. Some specific Honda models may require a 16mm socket, but a standard 5/8" spark plug socket often fits. You will also need a 10mm socket for the ignition coil bolts and a ratchet with extensions.
This video demonstrates how to replace spark plugs on a Honda Civic, including the tools needed: 49sSave Money TVYouTube · Jul 1, 2023

Tool	Description
Spark Plug Socket	Use a 14mm socket for newer Honda models (like 10th gen Civic) or a 5/8 inch (approx. 16mm) socket for older models (like 1.8L 2006-2015 Civic).
10mm Socket	Needed to remove the ignition coil bolts.
Ratchet	A 3/8 inch drive ratchet is common.
Extensions	You will likely need extensions to reach the spark plugs.

Why are spark plugs 14mm?

Additionally, 14mm thread size spark plugs have a higher copper core electrode, which provides better conductivity and a more efficient spark. This feature enhances the performance of the engine and helps save fuel. It also reduces emissions, making these spark plugs more environmentally friendly.

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.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.