What size is a Ford spark plug?
There isn’t a single universal size for Ford spark plugs. While most modern Ford engines use a 14 mm thread diameter, some older or specialty engines use different sizes such as 18 mm. Always verify the exact specification for your specific engine and model year before buying or installing plugs.
Understanding Ford spark plug sizes and why they vary
The term “size” for a spark plug encompasses several dimensions: thread diameter, thread length (the portion that screws into the cylinder head), reach (how far the plug extends into the combustion chamber), and the heat range. Ford’s current production engines predominantly use 14 mm threads, but there are exceptions depending on the engine family and generation. Using the wrong size can lead to cross-threading, improper sealing, or poor engine performance.
How to identify the correct spark plug size for your Ford
To ensure you get the right plug for your vehicle, follow these steps to determine the exact size and specifications needed.
- Check the owner's manual or the official Ford service/parts catalog for your exact engine code and year to confirm thread diameter and reach.
- Inspect the existing spark plug(s) removed from the engine. Look for markings on the plug’s threaded portion or on the box it came in; common thread diameters are 14 mm and 18 mm.
- Measure the thread diameter if you have the old plug out: use calipers to measure across the threads to verify the diameter (roughly 14 mm or 18 mm are typical in Ford cars).
- Identify the correct reach length by comparing the old plug’s threaded portion length to factory specifications. The reach must allow the electrode to sit in the combustion chamber correctly.
- Check the recommended heat range and gap for your engine in the service manual or a trusted parts database; Ford specifies a heat range appropriate for each engine.
- When in doubt, confirm with a dealer or a reputable parts retailer by entering your engine code or VIN to ensure you get the exact plug size and type.
Before you start, locate your vehicle’s engine code or VIN, as Ford often specifies different plugs for different engines within the same model year.
Having the correct size, heat range, and gap ensures proper ignition, fuel efficiency, and engine longevity.
Common sizes you might encounter in Ford engines
In practice, Ford’s modern lineup overwhelmingly uses 14 mm thread plugs, with a smaller subset of engines using 18 mm threads. The reach and heat range vary by engine family, so exact specifications should be checked for your particular model.
- 14 mm thread diameter: The most common size for many contemporary Ford engines (including many EcoBoost and Duratec variants).
- 18 mm thread diameter: Found on a minority of older or specialized Ford engines.
Always verify your exact engine specifications to avoid misfit plugs or damage to the cylinder head.
Summary
The short answer is: Ford spark plugs are not all the same size. The majority of today’s Ford engines use 14 mm threads, but some engines use 18 mm or other sizes. To be sure, consult your vehicle’s manual, check the engine code, inspect the existing plug, or consult a Ford dealer or parts database. Matching the thread size, reach, and heat range is essential for optimal performance and longevity.
What spark plugs does Ford use?
Ford uses its own brand, Motorcraft, for original equipment spark plugs, which are specifically designed for Ford vehicles. However, other brands like NGK and Autolite also manufacture spark plugs compatible with various Ford models. The exact spark plug depends on the specific vehicle, engine, and model year, so it is essential to check the vehicle's specifications.
Motorcraft
- Official brand: Ford Motor Company owns and operates the Motorcraft brand and recommends its original equipment spark plugs for its vehicles.
- Customized for Ford: These plugs are designed and engineered to be an exact fit for Ford, Lincoln, and Mercury vehicles.
- Variety: Motorcraft produces various spark plugs, such as the SP-452-X platinum spark plugs and CYFS-12-YEC or CYFS-12F-5 models.
Other compatible brands
- NGK: This brand makes compatible spark plugs for many Ford models, including NGK Iridium spark plugs for specific engines like the 3.5L EcoBoost, as noted in a YouTube video.
- Autolite: Ford acquired the Autolite trade name in 1961, and its products were originally standard equipment in Ford vehicles. Autolite XP Iridium spark plugs are available for Ford vehicles.
- Other brands: Other manufacturers also produce spark plugs that are compatible with Ford vehicles.
How to choose the right spark plug
- Check your owner's manual: This is the most reliable source for determining the correct spark plug for your vehicle.
- Consult an auto parts store: Professionals can help you find the right spark plug for your specific make, model, and year.
- Research your engine: Some modern engines, such as the 2021+ Ford F-150 3.5L EcoBoost, use specific plugs and require a precise installation process called "indexing" to ensure optimal performance.
What size are Ford 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 size socket is a Ford F-150 spark plug?
9/16 inch
Product Summary: OTC 6900 Ford F-150 Spark Plug Socket, Gray
This unique and patented design works on 2004–newer Ford F-150 pickup trucks with 5.4L 3-valve Triton V-8 engines. The socket end is 9/16 inch and the soft rubber insert holds and protects spark plug during removal and installation.
What size socket is a spark plug?
The most typical spark plug socket size is 5/8 inch ($16$mm), which is common in many newer vehicles and small engines. However, other common sizes include 13/16 inch ($20$mm) for older and larger engines, 9/16 inch ($14$mm) for many Ford, European, and Asian vehicles, and 3/4 inch ($18$mm or $19$mm) for some motorcycles and small engines. It's best to have a set of spark plug sockets to account for different vehicle makes and models.
You can watch this video to learn about the features of a spark plug socket: 1mDanny Johnson’s GarageYouTube · Aug 3, 2025
Common spark plug socket sizes
- 5/8 inch ($16$mm): The most common size for many newer cars and small engines.
- 13/16 inch ($20$mm): Often used for older and large-engine vehicles.
- 9/16 inch ($14$mm): Frequently found in Ford vehicles, as well as some newer European and Asian models.
- 3/4 inch ($18$mm or $19$mm): Used in motorcycles, small engines, and some older General Motors vehicles.
- Other sizes: Less common sizes like 11/16 inch ($18$mm) and 7/8 inch ($22$mm) are used in specific applications, such as older BMWs, motorcycles, tractors, and aviation engines.
