What size is an O2 sensor nut?

Oxygen sensors screw into the exhaust rather than being secured with a separate nut. The sizing you need to know is the thread size (most common: M18x1.5) and the wrench size used to turn the sensor (typically 22 mm). There are occasional variations, so always verify with your vehicle’s manual or the sensor’s documentation.

Thread size: the standard and its exceptions

The critical dimension is the threaded portion that mates with the exhaust. The most common standard across modern cars is M18x1.5. Some older vehicles or niche models use other thread sizes, so it’s important to double-check before purchasing a replacement sensor or an adapter.

• M18x1.5 — the prevailing size on most contemporary O2 sensors.


• M12x1.25 — encountered on a minority of older or European-specific applications.


• 1/2-20 UNF — present on a few older American applications or certain universal sensors.

In practice, M18x1.5 is by far the most widely used. If you are unsure, measure the thread with calipers or consult the vehicle's service manual or OEM part data.

Wrench size and turning the sensor

Beyond the thread, you need a wrench that fits the sensor's external hex in order to install or remove it. The standard hex size is typically 22 mm (7/8 in) across flats, though some models use a slightly different measurement.

• Common hex size to turn O2 sensors: 22 mm (7/8 in).


• Variations: Some brands or models may use 21–23 mm; a dedicated O2 sensor wrench helps in tight spaces.

When re-installing, follow the vehicle manufacturer's torque specification for the sensor to avoid under-tightening or over-tightening the threads. Do not rely on generic hardware torque values; precise specs vary by sensor and model. Note that OEM guidance often advises against applying extra anti-seize on the sensor threads unless specifically directed.

How to identify your exact size for replacement

To be sure you get the right sensor, check the exact thread size on your current sensor, refer to the vehicle's service manual, or look up the OEM part number for your make, model, and year. You can also bring the old sensor to a parts store to compare or use an online parts catalog that lists thread size by vehicle fitment.

1. Record year, make, model, and engine; pull the service manual or OEM parts data sheet for the correct O2 sensor thread size.


2. Inspect the sensor you’re replacing for any stamped thread size or part number; search the number online for exact specs.


3. Measure with calipers: note the thread diameter and pitch if the manual is unavailable.

In most cases, you will find M18x1.5 as the standard, with exceptions noted in the sources above. If you have a specific vehicle in mind, I can look up the exact size.

Summary

For the vast majority of vehicles, an O2 sensor threads into the exhaust with M18x1.5 threads and is tightened with a 22 mm wrench. Don’t assume a universal fit—verify your vehicle’s exact size from the service manual or OEM data. When in doubt, consult a professional or bring the sensor to a parts retailer to confirm the correct size before purchase or installation.

What size socket do I need to remove an O2 sensor?

The most common o2 sensor socket size is 7/8 inch (22mm), and it typically uses a 3/8-inch or 1/2-inch drive. These sockets are often designed with a side cutout to accommodate the wire harness, allowing for installation and removal without disconnecting the wire. 
Common o2 sensor socket sizes

• 7/8 inch (22mm): This is the most standard size for the sensor head. 
• 3/8-inch drive or 1/2-inch drive: This refers to the size of the drive that connects to your ratchet. Both are widely available. 

Key features of o2 sensor sockets

• Side cutout: A slot on the side of the socket allows the wire harness to pass through, so you don't have to disconnect the sensor before removal. 
• Offset design: Many sockets are offset, which provides better leverage in tight or hard-to-reach areas. 
• Universal fit: The 7/8" (22mm) size is considered a universal fit for most vehicles. 

Are all O2 sensors 22mm?

For most passenger vehicles, the standard O2 sensor socket sizes fall into three primary categories: 7/8-inch (22mm), 22mm, and the less common 22.5mm. Choosing the exact right one depends entirely on your specific vehicle's make, model, engine, and sensor location.

What size bolt is an O2 sensor?

The most common O2 sensor thread sizes are M18 x 1.5 for wideband sensors and M12 x 1.25 for narrow band sensors, but sizes can vary by vehicle. The hex head size for a standard O2 sensor is typically 7/8 inch (or 22 mm), which requires a specific oxygen sensor socket with a cutout to fit around the sensor's wiring harness. 
This video demonstrates how to install an O2 sensor and highlights the use of a 7/8 inch socket: 48sЈоhn “HEADSMASHER” DanielYouTube · Jul 12, 2023
Common thread sizes

• M18 x 1.5: Often used for wideband O2 sensors.
• M12 x 1.25: Commonly used for narrow band O2 sensors. 

This video shows the process of removing an O2 sensor and emphasizes the use of a special socket: 13sAuto Repair GuysYouTube · Aug 26, 2018
Common hex head size

• 7/8 inch (22 mm): This is the size for the hex head of most standard O2 sensors. You will need a specialized "O2 sensor socket" to remove it because it has a slot for the sensor's wiring. 
• Specialty socket: A standard wrench will not work on an O2 sensor with a harness. You need an O2 sensor socket that allows the wires to pass through while you turn the sensor. 

How to find the correct size for your vehicle

1. Check the vehicle's manual: Your car's owner's manual or repair manual will specify the correct size.
2. Inspect the old sensor: Before removing the old one, look for any markings on it that indicate the size.
3. Measure or research online: You can look up the specific year, make, and model of your vehicle to find the O2 sensor size online. 
4. Use a universal O2 sensor socket: If you are unsure of the exact size, a universal O2 sensor socket can be a good investment, as it is designed to fit a wide range of sensors and allows you to apply leverage to the hex head. 

What size is the O2 sensor nut?

The most common O2 sensor nut sizes are 7/8-inch (22mm) and 13/16-inch (21mm), requiring specialized wrenches like oxygen sensor sockets or crowsfoot wrenches designed specifically for the tight clearances and fragile nature of these sensors.