Can You Use a 7/8″ Socket on a 22 mm Fastener?

You generally should not use a 7/8″ (inch) socket on a 22 mm fastener, because while they are close in size, the small difference can cause slipping, rounding of the bolt or nut, and safety risks; a proper 22 mm socket is the correct tool. This question highlights the common confusion between metric and imperial sizes and whether they can be used interchangeably in automotive, mechanical, or DIY work.

Understanding the Size Difference

At first glance, 7/8″ and 22 mm seem almost identical, and in many toolboxes they are treated as “near equivalents.” However, in precision work, “almost the same” can be enough to damage hardware or tools.

Exact Measurements

To see why this matters, it helps to compare the measurements directly and understand how much play exists between the socket and the fastener head.

The following list explains the actual sizes and the gap between them.

• 7/8″ socket size (imperial): approximately 22.225 mm across flats
• 22 mm socket size (metric): exactly 22.000 mm across flats
• Difference between 7/8″ and 22 mm: about 0.225 mm (0.009″) larger for 7/8″
• Result: a 7/8″ socket will be slightly loose on a 22 mm nut or bolt head

While 0.225 mm seems tiny, the looseness is enough to increase wear on the corners of the fastener, especially under higher torque or repeated use.

Real-World Consequences of Using the Wrong Size

Using a socket that’s slightly too large can cause immediate or long-term issues, especially when working with tight, rusted, or high-torque fasteners commonly found in vehicles, machinery, or structural hardware.

Potential Damage and Safety Risks

The main concerns when using a 7/8″ socket on a 22 mm fastener are damage to the fastener, reduced grip, and potential injury from tool slippage.

The following list outlines the key risks involved.

• Rounding the fastener: The slight play allows the socket to twist on the corners of the nut or bolt, rounding them off and making removal or tightening difficult.
• Slippage under torque: When applying significant force (e.g., with a breaker bar or impact wrench), the loose fit increases the chance the socket will slip off suddenly.
• Injury risk: A slipping socket can cause knuckle injuries, loss of balance, or tool kickback, especially in tight spaces.
• Tool wear: Both the socket and the fastener head can wear prematurely, reducing reliability and accuracy of future work.
• Compounding problems: Once a head is slightly rounded by a loose socket, even the correct size may no longer grip properly, forcing the use of specialty extractors.

These risks become more serious as torque and frequency of use increase, making proper size selection more than just a matter of neatness or preference.

When People Still Use 7/8″ on 22 mm—and What That Means

Despite the drawbacks, many mechanics and DIYers occasionally use 7/8″ sockets on 22 mm fasteners, usually out of convenience or when the exact size is missing. This practice may work in some low-risk situations, but it is not best practice.

Situations Where It Might “Work” (But Isn’t Ideal)

There are scenarios where the mismatch is less likely to cause immediate failure, yet it remains a compromise that should be understood clearly.

The following list describes contexts where people sometimes get away with using a 7/8″ socket on a 22 mm fastener.

• Light torque applications: Gently tightening or removing a clean, lightly torqued fastener may not cause visible damage right away.
• Non-critical components: In non-structural or non-safety-critical assemblies, users may accept the risk for a one-time operation.
• Emergency situations: When the correct 22 mm socket is unavailable and work cannot be delayed, some will temporarily use 7/8″ as a workaround.
• Already worn fasteners: On slightly damaged heads, some users try near sizes hoping for any grip at all, although specialty extractor sockets are safer options.
• Hand tools only: If only low-force hand tools are used, the risk of immediate rounding or injury is reduced, though not eliminated.

Even in these cases, professionals generally regard this as an emergency or last-resort measure, not standard practice, and they usually correct it later with the proper metric socket.

Professional Recommendations and Best Practices

Tool manufacturers and professional mechanics consistently advise matching the socket size exactly to the fastener standard—metric to metric, imperial to imperial—to ensure both safety and quality of work.

What You Should Do Instead

Adopting a few simple rules can prevent most of the problems caused by mixing sizes and improve the long-term reliability of your tools and fasteners.

The following list presents recommended best practices for handling 22 mm fasteners.

• Use a 22 mm socket for 22 mm fasteners: This is the correct and safest choice, especially for automotive wheels, suspension, and structural components.
• Invest in full metric and imperial sets: Owning complete sets reduces the temptation to “get close” with the wrong standard.
• Avoid using 7/8″ on tight or rusted 22 mm bolts: For seized or high-torque fasteners, a precise fit is crucial to avoid rounding.
• Prefer six-point (hex) sockets for stubborn fasteners: Six-point sockets grip better and are less likely to round corners than twelve-point sockets, especially when sizes are exact.
• Use penetrating oil and proper technique: For hard-to-move fasteners, chemical and procedural help is safer than relying on a slightly oversized socket.

By following these practices, you greatly reduce the risk of damaging hardware, wasting time, or creating situations that require more specialized and expensive fixes later.

Key Takeaways on 7/8″ vs 22 mm

Although 7/8″ and 22 mm are very close in size, that small difference matters in practical use, especially where torque and safety are involved.

Practical Answer to the Original Question

The central question is whether you can use a 7/8″ socket in place of a 22 mm socket without causing problems, particularly in common tasks like working on vehicles or machinery.

The following list summarizes the most important points to remember.

• Fit difference: 7/8″ (≈22.225 mm) is slightly larger than 22 mm, so it will not fit as snugly.
• Risk: The loose fit increases the chance of rounding, slipping, and injury, especially at higher torque.
• Acceptability: It might work in low-torque, non-critical, or emergency situations, but it is not recommended as standard practice.
• Best practice: Always use a 22 mm socket for 22 mm fasteners whenever possible.
• Long-term view: Investing in and using the correct size protects both the fasteners and your tools, saving time and money over time.

Keeping these points in mind helps ensure safer and more reliable work, whether you are a professional mechanic or a home DIY enthusiast.

Summary

You technically can fit a 7/8″ socket over a 22 mm fastener, but you should not rely on it as a proper substitute. The 7/8″ socket is about 0.225 mm larger, which creates enough slack to increase the risk of rounding the nut or bolt and causing tool slippage, particularly under higher torque. While it may function in a pinch for low-stress, non-critical tasks, best practice is clear: use a correctly sized 22 mm socket for 22 mm fasteners to maintain safety, preserve hardware, and ensure professional-quality results.

Is 7, 8 or 22 mm smaller?

Wrench Conversion Chart – Metric to Standard (SAE/Inches)

Metric Size (mm)	Closest Standard Size	Difference
21mm	13/16″	+0.014″
22mm	7/8″	-0.009″
23mm	29/32″	-0.000″
24mm	15/16″	-0.007″

What size is equivalent to a 22mm socket?

A 22mm socket is equivalent to a 7/8 inch standard socket. While 7/8″ is the correct standard size, a 22mm socket can fit a 7/8″ fastener, and the reverse is also true, though it might be a bit snug.
 

• Conversion: 22mm≈0.86622 mm is approximately equal to 0.86622mm≈0.866 inches. 
• Standard Equivalent: 7/87 / 87/8 inch, which is exactly 0.8750.8750.875 inches. 
• Practical Use: You can use a 7/8″ socket on a 22mm fastener and vice versa, but be aware it’s not a perfect fit. 
  • A 7/8″ socket may feel slightly loose on a 22mm fastener. 
  • A 22mm socket may be a bit snug on a 7/8″ fastener. 

Is there a 22mm socket?

We carry 22 mm Sockets from top brands including TEKTON, Sunex Tools, Capri Tools and Husky. Check out our most reviewed product, the 1/2 in. Drive x 22 mm 6-Point Socket.

Can I use 7/8 socket for 22mm?

Yes, a 7/8″ socket can often be used for a 22mm bolt, as they are very close in size and often used interchangeably, though a 7/8″ is technically slightly larger. It’s best to use the correct size socket for the tightest fit and to avoid damaging the nut or bolt. 
Why a 7/8″ socket works on a 22mm bolt

• Close measurements: 7/8″ is equal to approximately 22.225mm, which is only a fraction larger than 22mm. 
• Interchangeable standard: In many cases, manufacturers consider these two sizes to be equivalent and may even stamp them on the same socket. 
• Common practice: It is a common practice to use one for the other, especially when a 22mm socket is unavailable. 

Potential downsides

• Loose fit: The 7/8″ socket may feel slightly loose on the 22mm bolt due to the small size difference. 
• Risk of damage: A slightly loose fit can increase the risk of stripping the bolt head, especially if it is already worn or if it’s a high-torque fastener. 

Best practice

• Use the correct size: For the best and safest fit, always use the socket that is the correct size for the bolt. 
• Consider a 22mm socket: If you plan on working with 22mm fasteners regularly, it is recommended to get a proper 22mm socket for the most precise and reliable fit. 
• Check for rust: If working on a vehicle, a 22mm lug nut can swell from rust, making it hard for a socket to fit. In such cases, a 7/8″ socket might be even looser.