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SAE-Metric Allen Wrenches

Allen Wrench
(Hex Key) Conversion -
Size Equivalence Chart

by Vaughn Aubuchon

This Allen wrench size conversion chart converts metric-sized wrenches to standard-sized wrenches, and shows which wrenches are roughly interchangeable. Not using the exact size hex key is not advised, because stripping can easily occur.
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Conversion Factors

Metric wrench sizes are shown, along with their "English Standard" equivalence, in 1/1000s of an inch. "Standard-size" wrenches refers to SAE sizes - the Society of Automotive Engineers.
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Allen Wrench Conversion
Table -
Hex Key Equivalent Sizes

Difference in 1/1000s of an inch
Size
in
Inches
Standard
SAE
Hex Key
Sizes

(inches)
Metric
Hex Key Sizes

(mm)

Notes - compares Standard and Metric Allen wrench sizes (where they MATCH, and where they don't - wrench equivalence)

-

-

15-key set
8-key set in yellow
15-key set

-

-

0.02756

0.7

Interchangable

0
0.028
0.028

7
0.035
0.035

Interchangable - -
1mm= 0.03937"

0
0.03543

0.9
4
0.03937

1.0

Also a standard size

10

0.04921

1.25

Also a standard size

1
0.050
0.050

Interchangable

1
0.05118

1.3
8
0.05905

1.5

-

3
0.06250
1/16

too small

16

0.07813
5/64

too big

1
0.07874

2

15

0.09375
3/32

-

5
0.09842

2.5

-

11
0.10937
7/64

-

9
0.11811

3

-

7
0.12500
1/8

-

12
0.13779

3.5

Also a standard size

3
0.14062
9/64

-

16

0.15625
5/32

 

Interchangable

1
0.15748

 

4

20

0.17716

4.5

-

10
0.18750
3/16

 

-

9
0.19685

 

5

-

19

0.21653

5.5

-

3
0.219
7/32

 

-

16

0.23622

 

6

-

16

0.250
1/4

 

-

25

0.27559

 

7

-

32

0.3125
5/16

 

-

2
0.31496

 

8

40

0.35433

 

9

Also a standard size

21

0.375
3/8

 

-

19

0.39370

 

10

 1cm= 0.39370"

Metric Set from Amazon -
0.7mm, 0.9mm, 1.3mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm
4.0mm, 4.5mm, 5.0mm, 5.5mm, 6.0mm, 7.0mm, 8.0mm, 10.0mm

SAE Set from Amazon -
.028",.035",.050", 1/16", 5/64", 3/32", 7/64",
1/8", 9/64", 5/32", 3/16", 7/32", 1/4", 5/16", and 3/8"

All the wrench sizes above were taken from Wikipedia at -
Hex Key - Wikipedia

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-

.
Larger Sizes

27
0.406
13/32

 

 -

4

0.433

11

Close enough (7/16 and 11mm)

31
0.438
7/16

 

4

0.469
15/32

 

Close enough (15/32 and 12mm)

28
0.472

 

12
12
0.500

1/2

 

 -

19
0.512

 

13

 -

20
0.531
17/32

 

 -

11
0.551

 

14

 -

28
0.563
9/16

 

 -

3

0.591

 

15

Close enough (19/32 and 15mm)

31
0.594
19/32

 Bicycle

5
0.625

5/8

 

?

26
0.630

 Bicycle

16

-

13
0.656
21/32

 

 -

18
0.669

 

17

 -

21
0.688
11/16

 

 -

10
0.709

 

18

 -

29
0.719
23/32

 

 -

2

0.748

 

19

Close enough (3/4 and 19mm)

31
0.750

3/4

 

6
0.781
25/32

 

 -

25
0.787

 

20

 -

14
0.813
13/16

 

 -

17
0.827

 

21

 -

22
0.844
27/32

 

 -

9
0.866

 

22

 -

11
0.875
7/8

 

 -

1

0.9055

 

none

Close enough (29/32 and 23mm)

31
0.9063
29/32

 

7
0.938
15/16

 

 -

55

0.945

 

24

 -

39

0.984

25

-

16

1.000
1

 -

  1"= 2.54cm (= 0.254m)

63

1.063

27

-

118

1.181

30

-

79

1.260

32

-

157

1.417

36

-

236

1.653

42

-

158

1.811

46

-

70

70

70

70

170 - 450


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Conversion Factors

English
to
Metric

1 inch =
1 inch =
1 inch =

2.54 centimeters
25.4 mm
0.0254 meters

1 foot =

30.48 cm

Metric
to
English

1 mm =

 0.03937 inches

1 cm =

0.3937 inches

1 meter =

39.37 inches

70

100

200 - 450

80



SAE Wrench Conversion

Many thanks to Bob V. for the dimension fix (2013-12-04).

DISCLAIMER
Although the author has tried to be as accurate as possible, errors are possible.

I could not find an online table like the above. So, I made this conversion chart, to help myself understand the relationships between wrench sizes of the metric system and wrench sizes of the standard system. I hope that it helps you.

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This Vaughns Allen Wrench Size Equivalence
Chart was last updated on 2018-06-06.