Hex Bolt and Nut Dimensions Chart (M3 to M36)
Hex bolt and nut chart, M3 to M36: width across flats s, head height k, across corners e, thread length b and nut height m. Letter labelled drawing, ISO 4014 and ISO 4032.
For preliminary reference and dimensional comparison. Tolerance ranges and property classes are not included. Confirm with the current edition of the standard and the manufacturer for orders, manufacture and tool selection.
Dimension drawing and symbols
- d
- Nominal diameter mm
- s
- Width across flats (nominal, max.) mm
- k
- Head height (nominal) mm
- e
- Width across corners, min., product grade A mm
- m
- Nut height, max. mm
- b
- Thread length mm
s is the width across flats, k the head height, e the width across corners, d the nominal diameter, b the thread length and m the nut height. b depends on the bolt length range l.
Columns
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| Bolt head, mm | Thread length b, mm | Nut, mm | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Size | dnominalmm | pitchmm | sacross flats | khead height | ee min. A | ee min. B | l ≤ 125 | 125 < l ≤ 200 | l > 200 | mnut height | nut e min. |
| M3 | 3 | 0.5 | 5.5 | 2.0 | 6.01 | 5.88 | 12 | 18 | 31 | 2.4 | 6.01 |
| M4 | 4 | 0.7 | 7.0 | 2.8 | 7.66 | 7.50 | 14 | 20 | 33 | 3.2 | 7.66 |
| M5 | 5 | 0.8 | 8.0 | 3.5 | 8.79 | 8.63 | 16 | 22 | 35 | 4.7 | 8.79 |
| M6 | 6 | 1 | 10.0 | 4.0 | 11.05 | 10.89 | 18 | 24 | 37 | 5.2 | 11.05 |
| M8 | 8 | 1.25 | 13.0 | 5.3 | 14.38 | 14.20 | 22 | 28 | 41 | 6.8 | 14.38 |
| M10 | 10 | 1.5 | 16.0 | 6.4 | 17.77 | 17.59 | 26 | 32 | 45 | 8.4 | 17.77 |
| M12 | 12 | 1.75 | 18.0 | 7.5 | 20.03 | 19.85 | 30 | 36 | 49 | 10.8 | 20.03 |
| M14 | 14 | 2 | 21.0 | 8.8 | 23.36 | 22.78 | 34 | 40 | 53 | 12.8 | 23.36 |
| M16 | 16 | 2 | 24.0 | 10.0 | 26.75 | 26.17 | 38 | 44 | 57 | 14.8 | 26.75 |
| M18 | 18 | 2.5 | 27.0 | 11.5 | 30.14 | 29.56 | 42 | 48 | 61 | 15.8 | 29.56 |
| M20 | 20 | 2.5 | 30.0 | 12.5 | 33.53 | 32.95 | 46 | 52 | 65 | 18.0 | 32.95 |
| M22 | 22 | 2.5 | 34.0 | 14.0 | 37.72 | 37.29 | 50 | 56 | 69 | 19.4 | 37.29 |
| M24 | 24 | 3 | 36.0 | 15.0 | 39.98 | 39.55 | 54 | 60 | 73 | 21.5 | 39.55 |
| M27 | 27 | 3 | 41.0 | 17.0 | no value | 45.20 | 60 | 66 | 79 | 23.8 | 45.20 |
| M30 | 30 | 3.5 | 46.0 | 18.7 | no value | 50.85 | 66 | 72 | 85 | 25.6 | 50.85 |
| M33 | 33 | 3.5 | 50.0 | 21.0 | no value | 55.37 | no value | 78 | 91 | 28.7 | 55.37 |
| M36 | 36 | 4 | 55.0 | 22.5 | no value | 60.79 | no value | 84 | 97 | 31.0 | 60.79 |
Quick answers
- M6 bolt: wrench size s 10 mm, head height k 4 mm, nut height m 5.2 mm, pitch 1 mm. View in table
- M8 bolt: wrench size s 13 mm, head height k 5.3 mm, nut height m 6.8 mm, pitch 1.25 mm. View in table
- M10 bolt: wrench size s 16 mm, head height k 6.4 mm, nut height m 8.4 mm, pitch 1.5 mm. View in table
- M12 bolt: wrench size s 18 mm, head height k 7.5 mm, nut height m 10.8 mm, pitch 1.75 mm. View in table
- M16 bolt: wrench size s 24 mm, head height k 10 mm, nut height m 14.8 mm, pitch 2 mm. View in table
- M20 bolt: wrench size s 30 mm, head height k 12.5 mm, nut height m 18 mm, pitch 2.5 mm. View in table
- M24 bolt: wrench size s 36 mm, head height k 15 mm, nut height m 21.5 mm, pitch 3 mm. View in table
Conditions and notes
ISO 4014:2011 hexagon head bolts, product grades A and B, ISO 4032 hexagon nuts style 1. Values compared from two manufacturer tables, they follow the ISO 4014:2011 edition.
- Each value is identical in two separate manufacturer tables. Differences seen in a third table (M5 grade A e, M6 and M24 nut height) did not replace the value shared by the two tables.
- Widths across flats of M10, M12, M14 and M22 differ from the older DIN 931 and DIN 934 sizes. Measure the wrench size on parts from old stock.
- Product grade A is not defined from M27 upwards. For M33 and M36 the length range l ≤ 125 mm does not exist.
- For fully threaded screws (ISO 4017) s, k and e are the same, the thread length b does not apply.
- The ISO 4014:2022 edition changes some b values (e.g. the range l ≤ 125 for M33 and l > 200 for M16 to M20). If you work to that edition, confirm the thread length in the standard. Nut values are the same as in ISO 4032:2023.
- CSV download is unavailable because the sources do not establish permission for reuse.
The width across flats s is the same for the bolt head and the nut. The head height k is the nominal value. For the width across corners e the minimum value given by the standard is shown, product grade A applies to short bolts up to M24 and product grade B to larger or longer bolts.
The thread length b takes three values depending on the bolt length range l. For l ≤ 125 mm b = 2d + 6, for 125 < l ≤ 200 mm 2d + 12 and for l > 200 mm 2d + 25 mm. An empty cell means that this length range is not defined for that size.
Sources
This table is for preliminary reference. Check the applicable standard and product conditions before use.
- Source 1. Version accessed. Accessed: 2026-10-16
- Source 2. Version accessed. Accessed: 2026-10-16
- Source 3. Version accessed. Accessed: 2026-10-16
- Source 4. Version accessed. Accessed: 2026-10-16
- Source 5. Version accessed. Accessed: 2026-10-16
Data version: 2026-10-16