Hex Key (Allen Wrench) Sizes (w/ Conversion Chart)

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It’s pretty much a given that when you buy anything from Ikea, it always comes with a bent, hex-shaped piece of metal that’s needed to make the screws fit. These tools are hex keys, although you may know them better as Allen wrenches and they can be found pretty much everywhere these days.

Unlike traditional Philips and straight heads, hex head fasteners are far less prone to stripping and are easier to secure. The keys are also more easily accessible than Torx bits. As a result they’ve become the preferred fastener type in many industries.

Common Hex Key Uses

assembly furniture with hex key

Furniture

As already mentioned, hex keys are used in most modern furniture where some assembly (and hair pulling) is required. Bed frames, dressers, tables, chairs, TV stands, and bookcases are just a few common pieces of furniture where hex keys are needed for assembly.

Automotive Industry

Allen keys are needed for many components on vehicles due to their ability to apply high torque without the risk of stripping the fastener. Fluid lines and brake calipers are just two of the many places you’ll need to use a key.

Electrical and Plumbing

From handheld devices to your kitchen faucet and garbage disposal, the compact head of a hex-shaped fastener make it easy to use when more traditional fasteners would be a tight fit.

Bicycles

Pretty much all of the fasteners used on bicycles these days are actually designed for use with a hex key.

Allen Wrench vs Hex Key

hex key sizes

Chances are, when you’re hunting for the best Allen wrench set, you’ll find some are specifically labelled Allen wrench and some are specified as hex keys. The difference is literally just in the name.

The phrase “Allen wrench” is actually trademarked and belongs to the company which invented them. Meanwhile, “hex key” is the generic term for the tool itself. It’s similar to how “Shop-Vac” is simply a specific brand of wet/dry vacuum.

Can You Use Something In Place of an Allen Wrench?

There are two common substitutes for when you’re missing the appropriate Allen key.

  1. Find a flat head screwdriver that will fit between two opposing points of the hex head. So long as you are gentle but firm, you can usually loosen the screw but may risk stripping the head.
  2. Alternately, you can try using a Torx bit that fits snugly into the hole. This can also strip the head, if you aren’t careful.

Short Arm vs Long Arm

Hex keys are surprisingly well-designed, despite being so simplistic in appearance. However, these little pieces of metal actually carry a secret if using one for the first time.

When you need superior leverage and torque, use the short end on the fastener. Need even more leverage? Use a long-arm hex key which essentially acts as a miniature breaker bar.

For areas that require a smaller turning arc, use a standard short-arm hex key and use the long end of the tool on the fastener. If you have limited space and require more torque, place a 10mm (or smaller) box end wrench over the short end of the hex to get better leverage.

Flat End vs Ball End

Most hex keys will be flat at both ends, but some will actually have a ball shape on one end. The ball end allows you to get into tighter spaces as they don’t need to go straight into the hole.

Once loosened, you can switch to the flat end to finish unscrewing the fitting.

T-Handle Hex Wrench Benefits

There are several variations on hex keys, from the aforementioned ball end to folding key sets that resemble Swiss army knives. However, the T-handle is perhaps the most useful variation out there.

These sets are T-shaped with the short end protruding from one side of the crossbeam. The intersection itself is larger and easy to grip, and is often made of insulating material to help reduce physical or electrical shock.

Because they’re easier to grip, they provide more torque than a regular hex key. Because of their length, you’ll need plenty of clearance above the fastener to use a T-handle hex.

Allen Wrench Sizes Chart

SAE SizeMetric SizeInches DecimalNote
0.7mm0.0230.028" and 0.7mm are
close enough
0.0280.028
0.035"0.0350.035" and 0.9mm are
close enough
0.9mm0.035
1mm0.039
1.25mm0.049
0.050"0.0500.05" and 1.3mm are
close enough
1.3mm0.050
1.5mm0.059
1/16"0.063
5/64"0.0785/64" and 2mm are
close enough
2mm0.079
3/32"0.094
2.5mm0.098
7/64"0.109
3mm0.118
1/8"0.125
3.5mm0.138
9/64"0.141
5/32"0.1565/32" and 4mm are
close enough
4mm0.157
4.5mm0.177
3/16"0.188
5mm0.197
5.5mm0.217
7/32"0.219
6mm0.236
1/4"0.25
7mm0.276
9/32"0.281
5/16"0.3135/16" and 8mm are
close enough
8mm0.315
9mm0.354
3/8"0.375
10mm0.394
13/32"0.406
11mm0.4337/16" and 11mm are
close enough
7/16"0.438
15/32"0.46915/32" and 12mm are
close enough
12mm0.472
1/2"0.500
13mm0.512
17/32"0.531
14mm0.551
9/16"0.563
15mm0.59115mm and 19/32" are
close enough
19/32"0.594
5/8"0.6255/8" and 16mm are
close enough
16mm0.630
21/32"0.656
17mm0.669
11/16"0.688
18mm0.709
23/32"0.719
19mm0.74819mm and 3/4" are
close enough
3/4"0.750
25/32"0.781
20mm0.787
13/16"0.813
21mm0.827
27/32"0.844
22mm0.866
7/8"0.875
23mm0.90623mm and 29/32" are
close enough
29/32"0.906
15/16"0.938
24mm0.945
25mm0.984
1"1.000
27mm1.063
30mm1.181
32mm1.260
36mm1.417
42mm1.654
46mm1.811

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