Allen Wrench Sizes

Standard Allen Wrench Sizes

If you’re looking for a list of every common Allen wrench size, you’ve found it. Our chart features all the regular-sized Allen wrenches for both SAE & metric. While large-sized Allen wrenches do exist, they are only used in a very specialized applications. Thus, sticking to the above list will suffice for even professional contractors & builders. At a first glance, the chart looks like it might be missing a few sizes. However, the “missing” sizes are rarely seen if they exist at all.

Precision Hex Sizes

On our list, we have six hex key sizes that we like to classify as precision hex sizes. They are primarily used in compact applications like electronics and aren’t seen in every industry. The precision SAE sizes are 0.028″, 0.035″, 0.05″ and the precision metric sizes are 0.7 mm, 0.9 mm, & 1.3 mm. Our take on these 6 Allen wrench sizes is that they should only be purchased if absolutely necessary for your work.

Common Metric Hex Key Sizes

In addition to the precision sizes mentioned above, the common metric Allen wrench sizes are 1.5 mm, 2 mm, 2.5 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 7 mm, 8 mm, 9 mm, & 10 mm. Of these sizes, some of the more popular ones are 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, & 10 mm.

Common SAE Hex Key Sizes

Adding to our precision sizes, the common SAE Allen wrench sizes are 1/16″, 5/64″, 3/32″, 7/64″, 1/8″, 9/64″, 5/32″, 3/16″, 7/32″, 1/4″, 5/16 “, & 3/8″. If we were to try to narrow down the Imperial sizes into a most popular list, it might include 1/8″, 3/32″, 7/64″, 5/32″, 3/16″, 1/4″, & 7/32″.

Less Common Metric Sizes

While these metric Allen key sizes do exist, they rarely appear in your basic Allen wrench sets. Their purpose is largely to serve specialized applications where size constraints and strength requirements need to be met. These sizes are 1 mm, 1.25 mm, 3.5 mm, 4.5 mm, 5.5 mm, & 7 mm.

Less Common SAE Sizes

This group of Allen wrenches are even less common than their metric counterparts. Reason being is that regular Imperial hex key sizes have a bit more coverage with the smaller sizes. Thus, most of the uncommon sizes are on the larger end of the spectrum. Chances are, you’ll never need to know these.

Please note—this chart is not a list of Allen wrench conversions. However, we do have one of those right here.