Metric to SAE Conversions for Allen Wrenches

Metric to SAE Conversions for Hex Keys

Metric to SAE Conversions for Hex Keys

Metric to SAE Conversions for Hex Keys Chart

Metric Hex Key SAE Hex Size
2 mm 3/32
2.5 mm 7/64
3 mm 1/8
3.5 mm 9/64
4 mm 5/32
5.5 mm 7/32
6 mm 1/4
7 mm 9/32
8 mm 5/16
9 mm 3/8


We are back at it again with another hex key size comparison. We’ve provided the best substitute metric Allen wrench for each given SAE size. But before you choose to reference this chart, you must know that we always recommend that you upgrade to a separate SAE Allen wrench set. With a sizable number of items still being produced in the United States, both metric and SAE hex key sets will be staples in your tool box.

Let’s start examining the Metric to SAE Conversions for Hex Keys chart. When you reference the Allen wrench size chart above, do be aware that using smaller size bits will increase your hardware’s vulnerability to stripping. Thus, we sometimes recommend trying a size above the one recommended in the chart to see if it’s a better fit. And you’ll want to be extra careful when working with precision hardware. Lastly, please remember that not every metric size has a perfect SAE counterpart. If you need a substitute for an Imperial size like 1/4″, you’re only option might be to get an SAE set with that wrench size. In any case, we hope you find this chart helpful and feel free to pass it along to other tool fanatics!

Pro Tips:

  • 9 mm can be used as a substitute for hex size 23/64″ as well as 3/8″
  • 5 mm works in place of hex size 13/64″, which isn’t included in most sets
  • 1.5 mm is a close substitute for hex size 1/16″, but use caution with sizes this small

Substituting Metric Allen Wrenches for SAE Sizes

With so many items manufactured in the United States, SAE hex screws are still prominent throughout the world. However, SAE hex wrenches are much harder to come by overseas than their metric counterparts are in North America. That’s where we step in—our guide for metric to SAE conversions for hex keys will save you time when working on your on the job. Just save it to your phone or bookmark this page in your browser for future reference.

Looking for an Imperial to Metric conversion chart for hex keys? We have you covered! Checkout our Allen wrench conversions guide for both metric & SAE.

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