What size spark plug socket for Ford Focus EcoBoost?

The vast majority of Ford Focus EcoBoost engines use a 16 mm (5/8 inch) spark plug hex, so a 16 mm spark plug socket is the standard tool to remove and install the plugs. This socket type grips the spark plug hex securely and is usually used with a magnetic or rubber insert to hold the plug during removal. Always confirm with your exact engine variant and model year, as there are a few exceptions.

In practice, this means that when you service a Focus EcoBoost—from the 1.0-liter three-cylinder to the 2.0-liter four-cylinder variants—the 16 mm spark plug socket, along with a short extension and a universal joint, will typically get you to the plugs. The rear bank or tight spots may require a flexible wand, but the socket size itself is typically 16 mm for most engines. This article covers the common scenario and provides practical steps and tools for a DIY plug swap.

Socket size and engine variants

To avoid confusion during a DIY plug change, use the following guidance to confirm the size and plan your toolkit. The focus is on the common 16 mm hex used by most EcoBoost engines in the Focus lineup.

• 16 mm spark plug socket (5/8 inch) with a rubber insert or magnetic adapter


• Short or medium extension to reach into the plug wells


• 3/8 inch drive ratchet (or 1/2 inch drive if space allows)


• Universal joint or flex joint for hard-to-reach plugs


• Torque reference or torque wrench for your engine’s specified setting

These tools cover the majority of Focus EcoBoost plug swaps, though some late-model or higher-performance variants may have slightly different arrangements or recommendations. Always verify by inspecting the old plug head or consulting the owner’s manual.

Steps to replace spark plugs

Below is a straightforward, step-by-step approach used by many DIY mechanics for a Focus EcoBoost spark plug replacement.

1. Identify and locate the spark plugs. On most Focus EcoBoost engines, the plugs sit under coil packs on each cylinder bank.


2. Disconnect the electrical connector from each ignition coil and release the coil by removing its bolt or clip as required by your engine variant.


3. Remove the ignition coil or coil pack to expose the spark plug well. Keep track of each coil to its cylinder to avoid misfiring later.


4. Clean the immediate area around the plug to avoid debris falling into the cylinder. Use compressed air if available.


5. Carefully thread out the old spark plug using the 16 mm socket with extension and a gentle, steady motion to avoid cross-threading.


6. Install the new spark plug by hand to ensure the threads engage cleanly, then tighten to the manufacturer’s torque specification, using a torque wrench for accuracy.


7. Reinstall the coil packs, reconnect electrical connectors, and double-check for secure seating. Refit any coverings or panels you removed.

Always follow Ford’s recommended torque specs for your exact engine variant and gap the plugs to the correct specification before installation.

Notes by model/year and rear-plug access

Rear-bank access and tool considerations

Some Focus EcoBoost configurations place rear plugs in tighter spaces, requiring a flexible extension or a wobble-type extension. If you encounter resistance or clearance issues, consider using a swivel head with your 16 mm socket and keeping extensions short to preserve control. When in doubt, consult the service manual for your exact model year and engine code.

Summary

The standard spark plug socket size for Ford Focus EcoBoost engines is 16 mm (5/8 inch), and this applies to the common 1.0L, 1.5L, and 2.0L EcoBoost variants found in Focus models across many years. Gather a 16 mm spark plug socket, a small extension, a swivel/joint, and a means to hold the plug, then follow the steps to replace the plugs with care, torque to spec, and reassemble. If you are unsure of your specific engine variant, verify with the owner’s manual or a trusted Ford service resource.

What size socket do you need to pull out 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 socket for EcoBoost spark plugs?

3/8" spark plug socket for EcoBoost engines, 14 mm.

What spark plugs for 3.5 EcoBoost?

The NGK 95605 spark plug is the top recommendation for Ford Ecoboost engines for several reasons. Material: Made from iridium, this plug is incredibly durable and can withstand high heat and electrical wear.

What size spark plugs for 1.5 EcoBoost?

Specifically designed for Ford EcoBoost 1.5L engines. Size: 14mm Bi-Hex (12pt) x 3/8"D x 180mm long.