Aaagh!!! We’ve all been there. You’ve got all your tools, you’re under the car, ready to work, and suddenly—S&T! It’s Imperial!*
So, what is a 10mm socket equivalent? The closest imperial size to a 10mm socket is a 3/8-inch socket.
Understanding Imperial and Metric Systems
Before we dive deeper, let’s clear up some confusion around measurement systems. Imperial sizes are also known as SAE (Society of Automotive Engineers) or Standard. Metric sizes, on the other hand, come from the SI (Système International) system, developed in France.
What is an Imperial Size (SAE)?
Imperial sizes are measured in inches or fractions of inches, such as 3/8 inch, 1/2 inch, or 7/16 inch. These sizes are typically used in the U.S. and the U.K., especially on older vehicles and tools.
Here’s a quick Imperial-to-Metric fastener chart for reference:
What is a Metric Size (SI)?
Metric fasteners are measured in millimetres (mm). The most common metric sizes in automotive work are M8, M10, and M12.
One important note: metric bolts are sized by thread diameter, not the head size. For example, an M8 bolt has a thread diameter of 8mm, requiring a 13mm socket to tighten the bolt head.
A Brief History of the Imperial and Metric Systems
Here’s where things get interesting. For centuries, most of the world used variations of the Roman measurement system, which eventually evolved into the Imperial system used in the UK and its colonies.
In 1795, after the French Revolution, France became the first country to adopt the metric system, creating a standard based on rational and universal units like meters and kilograms. Due to its simplicity and efficiency, the system spread across Europe over time. By the mid-19th century, most European countries had fully transitioned to the metric system.
The U.S. and Japan Join the Metric Movement
Although the U.S. has maintained widespread use of the Imperial system, American automakers like Ford, General Motors, and Chrysler began transitioning to metric measurements in the 1970s.
This was largely due to the rise of international trade and the influx of Japanese vehicles, which had already adopted metric fasteners in the 1920s.
In response, automakers formed the North American Automotive Metric Standards (NAAMS) to standardize measurements across the industry, making life much easier for parts suppliers and mechanics alike.
The UK’s Hybrid System
Meanwhile, the UK began its metrication process in the 1960s but has maintained a unique hybrid of both systems. British mechanics often work with a mix of metric and imperial tools, especially on vehicles manufactured during the transition period in the 1970s.
What Tools Should You Own?
Mechanics today primarily use metric tools. However, if you work on classic or vintage cars, keeping an imperial set on hand is a good idea. Here’s a breakdown of the essential tools I recommend:
Wrenches I’d Buy
If you’re looking for a solid set of ring wrenches, the TEKTON Combination Wrench Set is excellent. It comes in various sizes, but I recommend the 15-piece set to cover all your needs.
What makes these wrenches stand out is the 12-point ring design, which grips the fastener walls, not the edges. This is crucial when dealing with stubborn nuts and bolts. The chrome vanadium steel and mirror finish makes them durable and corrosion-resistant, and they’re clearly stamped for easy identification.
Ratcheting Wrenches, I’d Buy
Ratcheting wrenches are a lifesaver, especially in tight spaces. The GEARWRENCH 12-Point Ratcheting Wrench Set is my go-to.
With 72 teeth and a 5-degree arc, it’s perfect for those hard-to-reach fasteners that only turn a fraction of an inch at a time. The slim, strong head fits into tight spaces, and the lifetime warranty gives you peace of mind.
Check out the Amazon link below for deals on Gearwrench tools.
Amazon Gearwrench ToolsSocket Set I’d Buy
I’m a big fan of DeWalt tools. Their 192-piece Mechanics Tool Set has everything you need for both metric and imperial fasteners, with deep and regular sockets, as well as 1/4, 3/8, and 1/2-inch ratchets. The 72-tooth ratchets allow for precise control, and the set comes with a sturdy case to keep everything organized.
Check out the Amazon link below for hot deals on DeWalt kit.
Amazon DeWalt ToolsThink you know your tools inside and out?
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Related Questions
What size is between 10 and 11mm? A 3/8-inch wrench measures 9.53mm, while a 7/16-inch wrench measures 11.11mm.
Is M10 the same as 10mm? No, M10 refers to the thread diameter of the bolt, not the head size. An M10 fastener typically has a 17mm head and requires a 17mm socket or wrench.
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- About the Author
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.