An M10 bolt has a 1.5 mm coarse pitch, takes a 16 mm wrench (17 mm on older DIN 933 bolts) or an 8 mm hex key in a socket head cap screw, and fits an 11 mm clearance hole.
Metric bolt sizes M3 to M30: pitch, hex wrench size, socket head key and clearance holes
ISO metric bolts and screws, M3 to M30
Size
Coarse pitch (mm)
Fine pitch(es), ISO 262
Hex head wrench, ISO 4014/4017 (mm)
Hex head wrench, DIN 933 (withdrawn)
Socket head cap screw hex key (mm)
Key size standard
Clearance hole, ISO 273 fine (mm)
Clearance hole, ISO 273 medium (mm)
Clearance hole, ISO 273 coarse (mm)
M3
0.5
–
5.5
5.5
2.5
ISO 4762
3.2
3.4
3.6
M4
0.7
–
7
7
3
ISO 4762
4.3
4.5
4.8
M5
0.8
–
8
8
4
ISO 4762
5.3
5.5
5.8
M6
1
–
10
10
5
ISO 4762
6.4
6.6
7
M8
1.25
1
13
13
6
ISO 4762
8.4
9
10
M10
1.5
1.25, 1
16
17
8
ISO 4762
10.5
11
12
M12
1.75
1.5, 1.25
18
19
10
ISO 4762
13
13.5
14.5
M14
2
1.5
21
22
12
ISO 4762
15
15.5
16.5
M16
2
1.5
24
24
14
ISO 4762
17
17.5
18.5
M18
2.5
2, 1.5
27
27
14
DIN 912 (withdrawn)
19
20
21
M20
2.5
2, 1.5
30
30
17
ISO 4762
21
22
24
M22
2.5
2, 1.5
34
32
17
DIN 912 (withdrawn)
23
24
26
M24
3
2
36
36
19
ISO 4762
25
26
28
M27
3
2
41
41
19
DIN 912 (withdrawn)
28
30
32
M30
3.5
2
46
46
22
ISO 4762
31
33
35
ISO 4014/4017 and DIN 933 differ in wrench size at four sizes in this range: M10 (16 vs 17 mm), M12 (18 vs 19 mm), M14 (21 vs 22 mm) and M22 (34 vs 32 mm). The DIN column gives the DIN 933 (1987) widths across flats. DIN 933 is withdrawn and replaced by DIN EN ISO 4017; check the head before choosing a wrench.
Socket head key sizes are ISO 4762 values. ISO 4762:2004 does not list M18, M22 or M27; those rows give the withdrawn DIN 912 key size (14, 17 and 19 mm).
Fine pitches are those ISO 262 selects for bolts, screws and nuts. ISO 262 selects no fine pitch below M8; ISO 261 also lists 0.35 mm (M3), 0.5 mm (M4, M5) and 0.75 mm (M6).
ISO 273 clearance series are fine, medium and coarse, with tolerance fields H12, H13 and H14 given for information. ISO 273 recommends a chamfer where the hole edge would interfere with the underhead fillet.
The thread is written M, diameter and pitch in millimeters, such as M10 x 1.25. ISO 965-1 lets the pitch be left off for coarse threads, so M10 means the 1.5 mm coarse pitch. ISO 4014 designates a complete bolt by thread, nominal length and property class, for example Hexagon head bolt ISO 4014 - M12 x 80 - 8.8. In both ISO 4014 and ISO 4762 the length is measured from under the head to the end.
The property class comes from ISO 898-1 and is written as two numbers, such as 8.8, 10.9 or 12.9. The first number is one hundredth of the nominal tensile strength in N/mm2 (MPa), so 8.8 is an 800 MPa bolt. ISO 898-1 requires the class and the maker's mark on the head of hex head bolts and screws from M5 up, and of socket head cap screws from M5 up in class 8.8 and higher. FieldCharts does not publish tightening torques; use the fastener or equipment manufacturer's specification.
Wrench sizes: ISO and DIN differ at four sizes
ISO 4014 and ISO 4017 set the hex head width across flats for metric bolts and screws. DIN 933, the older German standard for fully threaded hex screws, has been withdrawn and replaced by DIN EN ISO 4017. From M3 to M30 the two differ at four sizes:
M10: 16 mm ISO, 17 mm DIN
M12: 18 mm ISO, 19 mm DIN
M14: 21 mm ISO, 22 mm DIN
M22: 34 mm ISO, 32 mm DIN
A 17 mm wrench fits a DIN 933 M10 head but not an ISO 4017 one, which takes 16 mm, so check the head before choosing a wrench. Sizes that are the same in both: M6 takes 10 mm, M8 13 mm, M16 24 mm, M20 30 mm and M24 36 mm.
Socket head cap screws
ISO 4762 sets the hex socket (Allen key) size for socket head cap screws: 2.5 mm for M3, 3 mm for M4, 4 mm for M5, 5 mm for M6, 6 mm for M8, 8 mm for M10, 10 mm for M12, 14 mm for M16, 17 mm for M20, 19 mm for M24 and 22 mm for M30. ISO 4762 does not list M18, M22 or M27; the withdrawn DIN 912 used 14, 17 and 19 mm keys for those.
The maximum head height of an ISO 4762 screw equals the thread diameter, and the maximum head diameter (plain head) is 10 mm for M6, 13 mm for M8 and 16 mm for M10. Allow for that when sizing a counterbore.
Clearance holes (ISO 273)
ISO 273 gives three clearance hole series for each thread size, fine, medium and coarse, and lists tolerance fields H12, H13 and H14 for them for information:
Fine: M6 6.4 mm, M8 8.4 mm, M10 10.5 mm.
Medium: M6 6.6 mm, M8 9 mm, M10 11 mm, M12 13.5 mm. TR Fastenings lists these medium sizes as its metric clearance holes.
Coarse: M6 7 mm, M8 10 mm, M10 12 mm.
The standard recommends a chamfer where the edge of the hole would otherwise interfere with the fillet under the bolt head. Optimas's chart lists 14 mm medium for M12; ISO 273 itself gives 13.5 mm, which the chart uses.
Coarse and fine pitch
Coarse pitch is the default: a callout without a pitch means coarse. ISO 262 selects the fine pitches used on bolts, screws and nuts: 1 mm for M8, 1.25 and 1 mm for M10, 1.5 and 1.25 mm for M12, 1.5 mm for M14 and M16, 2 and 1.5 mm for M18 to M22, and 2 mm for M24 to M30. It lists no fine pitch below M8, although the general plan in ISO 261 includes 0.35 mm for M3, 0.5 mm for M4 and M5, and 0.75 mm for M6. The full list by diameter is on the thread pitch chart, and the drill for each thread is on the tap drill chart.