Home FAQ

What size socket for 14mm spark plug?

The standard socket for a 14mm spark plug is typically a 9/16-inch spark plug socket, which corresponds closely to 14 mm in hex size. In practice, many tools are sold as “14mm spark plug sockets,” but the internal opening is usually 9/16 inch. Using the correct size helps prevent rounding and damage to the plug.

Understanding the correct size matters because spark plugs are measured by the hex across flats (the nut size on the plug), while sockets are sized in inches or millimeters. A socket that is too large can slip and strip the plug head; a socket that is too small won’t fit at all. For most passenger cars, a 3/8-inch drive is standard, while trucks may require a 1/2-inch drive for added leverage. In tight spaces, you may need a thin-wall design or flexible extensions to reach the plug safely.

Understanding the size and fit

To help you choose confidently, here are the key points about matching a socket to a 14mm spark plug and what features to look for in a socket set.

Common socket options and considerations:

Internal hex size: Most 14mm spark plugs are best served by a 9/16-inch (0.5625") spark plug socket, which is the closest practical inch-size match to the 14mm hex across flats. Some brands label the socket as “14mm” even though the internal opening is 9/16".

Drive size: Use a 3/8-inch drive for standard passenger cars; a 1/2-inch drive is common on larger engines or trucks where more torque is helpful.

End design: A rubber insert or magnetic sleeve helps hold the plug as you remove it, reducing the risk of dropping or dropping the plug into tight spaces.

Access in tight spaces: If the plug is recessed near the exhaust or in a cramped bay, consider a thin-wall socket and/or a swivel/rigid extension to improve reach without binding.

Concluding guidelines: For most engines with a 14mm spark plug, start with a 9/16-inch spark plug socket in a 3/8-inch drive. If you encounter clearance issues, switch to a thin-wall design, a magnetic retainer, and a wobble or universal joint extension to improve access without sacrificing grip.

Special considerations for tight spaces

In tightly packed engines, even the correct socket can struggle to seat properly. In those cases, a thin-wall socket, a flexible or wobble extension, and sometimes a shorter ratchet can make the difference between a successful removal and a slipped plug. Always ensure the plug head is clean and free of debris before loosening, and use gentle, steady pressure to avoid rounding the corners.

Practical steps for selecting and using the socket

Follow these steps to ensure you pick the right tool and remove the plug safely.

Verify the plug size on your engine: check the owner’s manual or inspect the plug hex across flats to confirm it matches the common 14mm specification.

Choose the socket that matches the plug: most 14mm plugs use a 9/16-inch hex opening; avoid using a larger 5/8-inch socket, which can distort the plug head.

Pick the right drive and extensions: 3/8-inch drive is standard; a 1/2-inch drive can help with high-torque scenarios for trucks.

Consider a thin-wall socket and a swivel or wobble extension for hard-to-reach plugs; add a magnetic or rubber-retainer insert for control.

Summary

For a typical 14mm spark plug, the recommended socket size is 9/16 inch, which aligns closely with the 14 mm hex across flats of the plug. Use a 3/8-inch drive for most cars, or 1/2-inch drive on larger engines, and consider thin-wall designs with a magnetic or rubber insert for easier handling in tight spaces. Always verify the specific plug size on your engine and consult the service manual if you’re unsure.

What size is a 14mm spark plug socket?

Size: 14mm Bi-Hex (12pt) x 3/8"D x 65mm long. Outside diameter: 17.88mm; inside depth: 61.7mm. Thin walled socket for use on modern engines with limited plug clearance. Fitted with rubber insert to protect and hold the spark plug.

What size is a M14 socket?

An M14 socket refers to a metric fastener with a 14mm thread diameter, and the corresponding socket size is typically 22mm for a standard hex head, though some specialized fasteners like triple square head bolts will have different socket sizes. Always confirm the specific socket needed for the fastener's head type, such as hex, triple square, or spline.

Socket Type	Corresponding Size
Standard Hex Head	22mm
Triple Square / Spline	Varies, but an "M14" designation for a socket means a size for a specific type of spline or triple square head

Standard Hex Head: For a typical M14 bolt or nut, you'll need a 22mm socket.
Specialized Heads: If the fastener has a different head type, like a triple square (XZN) or spline drive, an "M14" socket refers to the specialized bit size, which will be a different measurement from a standard hex socket.
Other types: Some M14 fasteners, like those in certain vehicles, may have a 17mm head, so it is important to verify the specific head type and size.

What can I use instead of 14mm?

Metric / Standard Wrench Conversion Chart

Bolt Diameter	Metric	Standard
3/8"	14mm	9/16"
7/16"	16mm	5/8"
1/2"	19mm	3/4"
9/16"	21mm	13/16"

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.