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What size spark plug socket Subaru?

For most Subaru engines, the standard spark plug socket size is 5/8 inch (16 mm). This size fits the common 14 mm spark plugs used in a wide range of Subaru models, from EJ to FA/FB families. Always verify against your specific model and year, but 5/8 inch is the rule of thumb for the majority of Subaru service procedures.

Subaru’s engine lineup includes several families (EJ, FA/FB, EZ, and others) with spark plugs that are typically 14 mm in thread diameter and use a compatible 5/8-inch socket. There are rare exceptions or aftermarket plugs that may require a different socket size, so when in doubt consult the service manual or check the exact plug you’re using before proceeding with removal or installation.

Common Spark Plug Socket Sizes for Subaru Engines

Below are the sizes you’re most likely to encounter. This helps you choose the right tool before you start the job.

5/8 inch (16 mm) spark plug socket — the standard choice for the vast majority of Subaru engines, including many EJ, FA, and FB models. Use with a rubber insert to hold the plug securely.

13/16 inch (approximately 21 mm) spark plug socket — occasionally required for certain unusual or aftermarket plugs; not common for stock Subaru engines. If a plug or manual specifies this size, use it instead of the standard 5/8 inch.

For nearly all Subaru maintenance tasks involving stock spark plugs, the 5/8 inch socket will be the correct tool. If you’re unsure, verify with your model’s service documentation or inspect the plug head to determine the appropriate hex size.

How to Confirm the Correct Size for Your Subaru

Before you buy or use sockets, follow these steps to ensure you’re using the right one for your engine and plug type.

Check the owner’s or service manual for the exact spark plug specification and tool recommendations for your engine code.

Look at the spark plug you’re removing or installing; note the hex size or the plug model number to confirm the correct socket size.

If in doubt, test-fit with a 5/8 inch socket first; if it doesn’t fit snugly, try a 13/16 inch socket on the plug head. Do not force a socket onto the plug.

Verifying the size before you begin can prevent cross-threading or damaging plugs. If you’re working in a tight engine bay, a flexible extension or a swivel joint can help you align the socket without stressing the plug.

Tools and Setup for Subaru Spark Plug Service

A well-equipped toolbox makes plug replacement quicker and safer. The following gear is typically recommended for Subaru engines.

Spark plug socket with rubber insert (5/8 inch, 16 mm) and a comfortable grip

3/8-inch drive ratchet or 1/2-inch drive ratchet, depending on space and leverage

Extension bars and a universal joint for hard-to-reach plugs

Torque wrench to apply the manufacturer’s recommended torque

Anti-seize compound and dielectric grease as appropriate

With the right socket, extensions, and torque control, you’ll complete a Subaru spark plug change efficiently and safely.

Summary

In most Subaru models, the go-to spark plug socket size is 5/8 inch (16 mm), designed to fit the common 14 mm plugs used across the EJ, FA, and FB engine families. Always verify against your specific model/year and plug specification. If you encounter an unusual plug, a 13/16 inch socket may be required, but this is not typical. Prepare with the right tools, follow the service manual, and you’ll be ready for a smooth spark plug service. Finally, a tidy, properly torqued installation helps maintain engine performance and longevity.

What size socket is a Subaru spark plug?

The Subaru spark plug socket size is 14mm for most modern vehicles (FA/FB engines, 2011 and later), while older EJ engines typically use a 16mm socket. You will need a thin-walled spark plug socket, and a magnetic or swivel type is highly recommended to make removal easier due to the tight space.
This video demonstrates the tools and techniques used to replace spark plugs on a Subaru, including the use of a 14mm spark plug socket: 53sDaryl TurcottYouTube · Jun 11, 2023
Socket size by engine type

For most modern Subarus (2011 and newer, FA/FB engines): Use a 14mm socket.
For older Subarus (pre-2011, EJ engines): Use a 16mm socket.

Other tips

Thin-walled: A thin-walled socket is often necessary to fit in the tight spaces between the engine and the spark plug well.
Magnetic or swivel: A socket with a built-in magnet or swivel is highly recommended, as it helps hold the plug and makes it easier to retrieve from the engine bay.
Drive size: Subaru spark plug sockets are commonly available in 3/8-inch drive.
Confirm with owner's manual: If possible, always double-check your vehicle's owner's manual for the exact specifications.

What size socket do I need to pull a spark plug?

The most common socket sizes for spark plugs are 5/8 inch (16mm) and 13/16 inch (20mm), but other sizes like 9/16 inch (14mm) and 3/4 inch (18mm) are also used depending on the vehicle. The exact size depends on the make, model, and age of your vehicle. You may need to check your vehicle's manual or measure the spark plug to find the correct size.
Common spark plug socket sizes

5/8 inch (16mm): The most common size, used in many modern and small-engine vehicles, as well as motorcycles.
13/16 inch (20mm): Often used in older and larger-engine vehicles.
9/16 inch (14mm): Frequently found in Ford vehicles, newer European and Asian cars, and some motorcycles.
3/4 inch (18mm): Used in some motorcycles, small engines, and older GM vehicles.
11/16 inch (18mm): Used in some motorcycles, small engines, and older BMW vehicles.

You can watch this video to learn about different socket sizes and how to use them: 1mDanny Johnson’s GarageYouTube · Aug 3, 2025
Tips for choosing the right socket

Consult your vehicle's manual: This is the most reliable way to find the correct size.
Measure the spark plug: You can measure the hexagonal part of the spark plug to find its size.
Look for a "spark plug socket": These are specifically designed for spark plugs and often have a rubber insert to protect the porcelain insulator and hold the plug in place.

This video demonstrates how to use spark plug sockets: 51sbeachtrollYouTube · Sep 7, 2018

What size spark plug socket for 2015 Subaru Forester?

The spark plug socket size for a 2015 Subaru Forester is a 14mm deep socket, ideally one with a magnetic or rubber insert to hold the plug. You will also need a 3/8" drive and may need wobble extensions to access the plugs due to tight clearance.
This video demonstrates how to remove spark plugs from a Subaru Forester: 1m1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · Jul 16, 2018

Socket size: 14mm
Socket type: Deep, thin-walled socket with a magnetic or rubber insert to hold the spark plug
Drive: 3/8"
Extensions: Wobble extensions are recommended due to the tight working space

What size socket for 2010 Subaru Forester spark plugs?

The driver's side is very similar. Almost as easy the only difference is on the driver's side it's a lot easier to reach the back one.

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.