Tool Diameter in mm.

Thread Size     Steel     Stainless Steel
M3X0.5
2.7
2.7
M4X0.7
3.7
3.7
M5X0.8
4.5
4.6
M6X1.0
5.3
5.4
M8X1.25
7.3
7.4
M10X1.5
9.2
9.3
M12X1.75
10.9
10.9
M14X2.0
13.0
13.0
M16X2.0
14.8
14.8
M18X2.5
16.7
16.7
M20X2.5
18.7
18.7
BSP
1/8BSP
9.2
9.2
1/4 BSP
12.4
12.4
3/8 BSP
15.9
15.9
1/2 BSP
19.9
19.9
3/4 BSP
25.4
25.4
1/1 BSP
31.9
31.9
UNC
N5 UNC (40)
2.9
2.9
N6 UNC (32)
3.1
3.1
N8 UNC (32)
3.8
3.8
N10 UNC (24)
4.3
4.3
N12 UNC (24)
4.9
4.9
1/4 UNC (20)
5.7
5.7
5/16 UNC (18)
7.2
7.2
3/8 UNC (16)
8.7
8.7
7/16 UNC (14)
10.2
10.2
1/2 UNC (13)
11.7
11.7
9/16 UNC (12)
13.2
13.2
5/8 UNC (11)
14.7
14.7
3/4 UNC (10)
17.8
17.8
M6X0.75
5.6
5.6
M6X0.5
5.8
5.8
M8X1.0
7.5
7.5
M8X0.75
7.6
7.6
M10X1.25
9.3
9.3
M10X1.0
9.5
9.5
M12X1.5
11.2
11.2
M12X1.0
11.5
11.5
M16X1.5
15.2
15.2
M16X1.0
15.5
15.5
M18X1.5
17.2
17.2
UNF
N5 UNF (44)
2.9
2.9
N6 UNF (40)
3.2
3.2
N8 UNF (36)
3.9
3.9
N10 UNF (32)
4.4
4.4
N12 UNF (28)
5.0
5.0
1/4 UNF (28)
5.9
5.9
5/16 UNF (24)
7.4
7.4
3/8 UNF (24)
9.0
9.0
7/16 UNF (20)
10.4
10.4
1/2 UNF (20)
12.1
12.1
9/16 UNF (18)
13.6
13.6
5/8 UNF (18)
15.2
15.2
3/4 UNF (16)
18.3
18.3
NPT