ToolBox

Inch (fraction) vs. metric: Measures and tools

The following table (Table 1) gives an overview of the most important inch dimensions in fractions, their conversion into millimeters and the corresponding wrench sizes for AF tools ("Across Flats") in millimeters.

Nominal measure
Inch [in]

Conversion base
Inch [in]

Equivalent in
Millimeters [mm]

Inch-AF-Tools
Effective wrench size [mm]

14

832

6.35

6.40

516

1032

7.94

8.03

1132

1132

8.73

8.81

38

1232

9.53

9.60

1332

1332

10.32

10.39

716

1432

11.11

11.18

12

1632

12.70

12.80

916

1832

14.29

14.38

1932

1932

15.08

15.18

58

2032

15.88

15.98

2132

2132

16.67

16.77

1116

2232

17.46

17.58

34

2432

19.05

19.18

2532

2532

19.84

19.97

1316

2632

20.64

20.78

78

2832

22.23

22.35

1516

3032

23.81

23.98

1

3232

25.40

25.55

1 116

1 232

26.99

27.13

1 18

1 432

28.58

28.75

1 316

1 632

30.16

30.34

1 14

1 832

31.75

31.93

Table 1) The most important inch dimensions, their conversion into millimeters and the corresponding wrench sizes for AF tools

Table 2 gives an overview of the equivalent spanner sizes for different systems (metric; inch: Across-Flats (AF), Whitworth, BA). Example: A 5/16\" AF spanner can be replaced with an 8 mm spanner.

AF – mm

mm – Whitworth

mm – BA

AF – Whitworth

5 = 6BA

7 = 3BA

516 = 8

8 = 2BA

9 = 1BA

1132 = 18

716 = 11

58 = 16

18 = 38

21 = 716

78 = 22

1516 = 24

1 = 916

1 116 = 27

28 = 58

The tables can also be downloaded as a PDF file:

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