SAE and Metric Wrench and Socket Size Reference
In combined wrench sets, manufacturers often provide a single wrench for sizes that are very close (typically within 0.05 mm or less) to avoid redundancy. SAE (Society of Automotive Engineers) is often referred to as "standard" as opposed to the alternative "metric" size standard.
Common Wrench Sizes
- Standard (SAE): Common sizes in inches: 1/4, 5/16, 11/32, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4, 13/16, 7/8, 15/16, 1, 1-1/16, 1-1/8, 1-1/4.
- Metric: Common sizes in mm: 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 27, 30, 32.
combined sets where one wrench serves both sizes:
- 19 mm and 3/4 inch (19.05 mm, difference 0.05 mm)
- 27 mm and 1-1/16 inch (26.9875 mm, difference 0.0125 mm)
Other pairs (e.g., 6 mm and 1/4 inch, 8 mm and 5/16 inch) have differences >0.05 mm and are typically included separately in combined sets
| Size | Type | Size (mm) | Notes on Approximate Matches |
|---|---|---|---|
| 6 mm | Metric | 6.00 | Close to 1/4 inch (0.35 mm difference) |
| 1/4 inch | SAE | 6.35 | Close to 6 mm (0.35 mm difference) |
| 7 mm | Metric | 7.00 | |
| 8 mm | Metric | 8.00 | Close to 5/16 inch (0.0625 mm difference) |
| 5/16 inch | SAE | 7.9375 | Close to 8 mm (0.0625 mm difference) |
| 11/32 inch | SAE | 8.73125 | |
| 9 mm | Metric | 9.00 | |
| 3/8 inch | SAE | 9.525 | Close to 10 mm (0.475 mm difference) |
| 10 mm | Metric | 10.00 | Close to 3/8 inch (0.475 mm difference) |
| 11 mm | Metric | 11.00 | Close to 7/16 inch (0.1125 mm difference) |
| 7/16 inch | SAE | 11.1125 | Close to 11 mm (0.1125 mm difference) |
| 12 mm | Metric | 12.00 | |
| 1/2 inch | SAE | 12.7 | Close to 13 mm (0.3 mm difference) |
| 13 mm | Metric | 13.00 | Close to 1/2 inch (0.3 mm difference) |
| 14 mm | Metric | 14.00 | |
| 9/16 inch | SAE | 14.2875 | |
| 15 mm | Metric | 15.00 | |
| 5/8 inch | SAE | 15.875 | Close to 16 mm (0.125 mm difference) |
| 16 mm | Metric | 16.00 | Close to 5/8 inch (0.125 mm difference) |
| 17 mm | Metric | 17.00 | |
| 11/16 inch | SAE | 17.4625 | |
| 18 mm | Metric | 18.00 | |
| 19 mm | Metric | 19.00 | Approximately the same as 3/4 inch (0.05 mm difference) |
| 3/4 inch | SAE | 19.05 | Approximately the same as 19 mm (0.05 mm difference) |
| 20 mm | Metric | 20.00 | |
| 21 mm | Metric | 21.00 | Close to 13/16 inch (0.3625 mm difference) |
| 13/16 inch | SAE | 20.6375 | Close to 21 mm (0.3625 mm difference) |
| 22 mm | Metric | 22.00 | Close to 7/8 inch (0.225 mm difference) |
| 7/8 inch | SAE | 22.225 | Close to 22 mm (0.225 mm difference) |
| 15/16 inch | SAE | 23.8125 | Close to 24 mm (0.1875 mm difference) |
| 24 mm | Metric | 24.00 | Close to 15/16 inch (0.1875 mm difference) |
| 1 inch | SAE | 25.4 | |
| 1-1/16 inch | SAE | 26.9875 | Approximately the same as 27 mm (0.0125 mm difference) |
| 27 mm | Metric | 27.00 | Approximately the same as 1-1/16 inch (0.0125 mm difference) |
| 1-1/8 inch | SAE | 28.575 | |
| 30 mm | Metric | 30.00 | |
| 1-1/4 inch | SAE | 31.75 | Close to 32 mm (0.25 mm difference) |
| 32 mm | Metric | 32.00 | Close to 1-1/4 inch (0.25 mm difference) |
In combined wrench sets, only one wrench is typically provided for: 19 mm / 3/4 inch (19 mm and 19.05 mm) and 27 mm / 1-1/16 inch (27 mm and 26.9875 mm) because the difference is less than 0.05 mm. Other pairs like 6 mm / 1/4 inch, 8 mm / 5/16 inch, 10 mm / 3/8 inch, 11 mm / 7/16 inch, 13 mm / 1/2 inch, 16 mm / 5/8 inch, 21 mm / 13/16 inch, 22 mm / 7/8 inch, 24 mm / 15/16 inch, and 32 mm / 1-1/4 inch are close but typically included separately in combined sets due to differences >0.05 mm. These may be used interchangeably in non-precision applications.
The SAE (Society of Automotive Engineers) size system, based on fractions of an inch, originated in the United States and became the standard for tools and fasteners in the early automotive industry, particularly in the U.S. during the early 20th century. As American automakers like Ford and General Motors mass-produced vehicles, SAE sizes (e.g., 1/4 inch, 3/8 inch, 1/2 inch) were widely adopted for bolts, nuts, and wrenches due to their alignment with the inch-based system prevalent in U.S. manufacturing. This standardization ensured compatibility across vehicles and tools, simplifying production and repairs.
The introduction of metric sizes in the automotive industry began gaining traction in the 1960s and 1970s, driven by global trade and the increasing presence of foreign automakers, particularly from Europe and Japan (e.g., Volkswagen, Toyota), where the metric system was standard. By the late 1970s, the U.S. automotive industry started transitioning to metric fasteners to align with international standards, reduce production costs, and facilitate exports. For example, General Motors began incorporating metric sizes in the 1970s, with vehicles like the 1980s GM models using both SAE and metric fasteners during the transition. By the 1990s, most new vehicles globally, including in the U.S., predominantly used metric sizes (e.g., 10 mm, 13 mm) for consistency, though some American vehicles retained SAE fasteners for specific components.
Today, modern vehicles are almost entirely metric, reflecting global manufacturing standards, but SAE tools remain relevant for older American cars and certain specialty applications. Mechanics often need both SAE and metric wrench sets due to this mixed legacy, with combined sets addressing close sizes (e.g., 19 mm and 3/4 inch) to handle both systems efficiently.