This bolt size chart provides detailed dimensions for ISO metric hex head screws and nuts, including thread sizes, pitch, and standard specifications. The tables cover sizes from M3 to M36 with both coarse and fine thread series, making this a practical reference for engineers, designers, and workshop use.
Quick Answer: Metric bolt sizes range from M3 to M36 with standard thread pitches and defined dimensions for head size, pitch diameter, and nut compatibility as per ISO standards.
Notes:
The screw and nut sizes are in accordance with BS 3692:1967 (ISO 272 equivalent).
This standard has now been superseded by BS 3692:2001. (The data has not yet been checked against
the latest revision. ). The thread form is in accordance with BS 3643:2007
All dimensions in millimetres
BS 3643 Part 1:2007..ISO metric screw threads. Principles and basic data
BS 3643 Part 2:2007..ISO metric screw threads. Specification for selected limits of size
BS 3692:2001..ISO metric precision hexagon bolts, screws and nuts. Specification
Use these calculators with the hex bolt, nut and washer dimensions on this page for practical fastener selection and layout checks.
| Calculator | Use |
| Bolt Head and Nut Clearance Calculator | Check spanner or socket access around a hex bolt head or nut. |
| Bolt Length Calculator | Estimate required bolt length for through bolts and tapped holes. |
| Washer Bearing Pressure Calculator | Calculate bearing pressure under washers, nuts and bolt heads. |
| Bolt Hole Clearance Calculator | Calculate clearance between a bolt shank and clearance hole. |
| Bolt Tightening Torque Calculator | Calculate tightening torque from target preload. |
| Bolted Joint and Fastener Calculators | View all RoyMech bolt, screw and fastener calculators. |
| Nominal (D) | Thread. | Bolt dia | Bolt Head | Bolt Nut | |||
| Size | Pitch | Major(d) max - min |
Minor(d3 ) max - min |
Pitch Diameter (d2 ) max - min |
Thick (Zb) | Acc/Flats (A/F) max - min |
Acc./Corn (A/C) |
| M3 | 0,5 | 2,980 - 2,874 | 2,439 -2,272 | 2,655 - 2,580 | 2,125 | 5,50 - 5,38 | 6,40 |
| M4 | 0,7 | 3,978 - 3,838 | 3,220 - 3,002 | 3,523 - 3,433 | 2,925 | 7,00 - 6,85 | 8,10 |
| M5 | 0,8 | 4,976 - 4,826 | 3,869 - 4,110 | 4,456 - 4,361 | 3,650 | 8,00 - 7,85 | 9,20 |
| M6 | 1,0 | 5,974 - 5,794 | 4,891 - 4,596 | 5,324 - 5,212 | 4,150 | 10,00 - 9,78 | 11,50 |
| M8 | 1,25 | 7,972 - 7,760 | 6,272 - 6,619 | 7,160 - 7,042 | 5,650 | 13,00 - 12,73 | 15,00 |
| M10 | 1,5 | 9,968 - 9,732 | 8,344 - 7,938 | 8,994 - 8,862 | 7,180 | 17,00 - 16,73 | 19,60 |
| M12 | 1,75 | 11,966 - 11,701 | 10,072 - 9,601 | 10,829 - 10,679 | 8,180 | 19,00 - 18,67 | 22,10 |
| M16 | 2,0 | 15,962 - 15,682 | 13,797 - 13,271 | 14,663 - 14,503 | 10,180 | 24,00 - 23,67 | 27,70 |
| M20 | 2,5 | 19,958 - 19,623 | 17,252 - 16,624 | 18,334 - 18,164 | 13,215 | 30,00 - 29,67 | 34,60 |
| M24 | 3,0 | 23,952 - 23,577 | 20,701 - 19,955 | 22,003 - 21,803 | 15,215 | 36,00 - 35,58 | 41,60 |
| M30 | 3,50 | 29,947 - 29,522 | 26,158 - 25,306 | 27,674 - 27,462 | 19,260 | 46,00 - 45,38 | 53,1 |
| M36 | 4,00 | 35,940 - 35,465 | 31,610 - 30,654 | 33,342 - 33,118 | 23,260 | 55,00 - 54,26 | 63,5 |
Nut tolerance class 6H are dimensioned in BS3692
Thread form to BS 3643
| Nominal | Thread. | Nut Diameter | Nut | |
| Size | Pitch | Major (D) | Minor (D1 ) Max - min |
Thick (Zn) |
| M3 | 0,5 | 3,000 | 2,599 - 2,459 | 2,40 |
| M4 | 0,7 | 4,000 | 3,422 - 3,242 | 3,20 |
| M5 | 0,8 | 5,000 | 4,334 - 4,134 | 4,00 |
| M6 | 1,0 | 6,000 | 5,153 - 4,917 | 5,00 |
| M8 | 1,25 | 8,000 | 6,912 - 6,647 | 6,50 |
| M10 | 1,5 | 10,000 | 8,676 - 8,376 | 8,00 |
| M12 | 1,75 | 12,000 | 10,441 - 10,106 | 10,00 |
| M16 | 2,0 | 16,000 | 14,210 - 13,835 | 13,00 |
| M20 | 2,5 | 20,000 | 17,744 - 17,294 | 16,00 |
| M24 | 3,0 | 24,000 | 21,252 - 20,752 | 19,00 |
| M30 | 3,5 | 30,000 | 26,771 - 26,211 | 24,00 |
| M36 | 4,0 | 36,00 | 32,270 - 31,670 | 29,00 |
Bolt tolerance class 6g are dimensioned in BS3692:1967
| Nominal | Thread. | Bolt dia (d) | Bolt Head | Bolt Nut | |||
| Size | Pitch | Major max - min |
Minor max - min |
Pitch Diameter max - min |
Thick (Zb) | Acc/Flats max - min (A/F) |
Acc./Corn (A/C) |
| M6 | 0,75 | 5,978 - 5,838 | 5,166 - 4,929 | 5,491 - 5,391 | 4,150 | 10,00 - 9,78 | 11,50 |
| M8 | 1,00 | 7,974 - 7,794 | 6,891 - 6,596 | 7,324 - 7,212 | 5,650 | 13,00 - 12,73 | 15,00 |
| M10 | 1,25 | 9,972 - 9,760 | 8,619 - 8,272 | 9,160 - 9,042 | 7,180 | 17,00 - 16,73 | 19,60 |
| M12 | 1,25 | 11,972 - 11,760 | 10,619 - 10,258 | 11,160 - 11,028 | 8,180 | 19,00 - 18,67 | 22,10 |
| M16 | 1,50 | 15,968 - 15,732 | 14,344 - 13,930 | 14,994 - 14,854 | 10,180 | 24,00 - 23,67 | 27,70 |
| M20 | 1,5 | 19,968 - 19,732 | 18,344 - 17,930 | 18,994 - 18,854 | 13,215 | 30,00 - 29,67 | 34,60 |
| M24 | 2,0 | 23,962 - 23,682 | 21,797 - 21,261 | 22,663 - 22,493 | 15,215 | 36,00 - 35,58 | 41,60 |
| M30 | 2,0 | 29,962 - 29,682 | 27,797 - 27,261 | 28,663 - 28,493 | 19,260 | 46,00 - 45,38 | 53,1 |
| M36 | 3,00 | 35,952 - 35,577 | 32,704 - 31,955 | 34,003 - 33,803 | 23,260 | 55,00 - 54,26 | 63,5 |
Nut tolerance class 6H are dimensioned in BS3692:1967
| Nominal | Thread. | Nut Diameter | Nut | |
| Size | Pitch | Major | Minor Max - min |
Thick (Zn) |
| M6 | 0,75 | 6,000 | 5,378 - 5,188 | 5,00 |
| M8 | 1,00 | 8,000 | 7,153 - 6,917 | 6,50 |
| M10 | 1,25 | 10,000 | 8,912 - 8,647 | 8,00 |
| M12 | 1,25 | 12,000 | 10,912 - 10,647 | 10,00 |
| M16 | 1,50 | 16,000 | 14,676 - 14,376 | 13,00 |
| M20 | 1,50 | 20,000 | 18,676 - 18,376 | 16,00 |
| M24 | 2,0 | 24,000 | 22,210 - 21,835 | 19,00 |
| M30 | 2,0 | 30,000 | 28,210 - 27,835 | 24,00 |
| M36 | 3,0 | 36,00 | 33,252 - 32,752 | 29,00 |
Bright Washers are dimensioned in BS4320: 1968
| Nominal | Washer Diameter | Washer Thickness | ||
| Size | Internal max - min |
External max - min |
Thick max - min |
Thin |
| M3 | 3,4 - 3,2 | 7,0 - 6,7 | 0,6 - 0,4 | - |
| M4 | 4,5 - 4,3 | 9,0 - 8,7 | 0,9 - 0,7 | - |
| M5 | 5,5 - 5,3 | 10,0 - 9,7 | 1,1 - 0,9 | - |
| M6 | 6,7 - 6,4 | 12,5 - 12,1 | 1,8 - 1,4 | 0,9 - 0,7 |
| M8 | 8,7 - 8,4 | 17,0 - 16,6 | 1,8 - 1,4 | 1,1 - 0,9 |
| M10 | 10,9 - 10,5 | 21,0 - 20,5 | 2,2 - 1,8 | 1,45 - 1,05 |
| M12 | 13,4 - 13,0 | 24,0 - 23,5 | 2,7 - 2,3 | 1,8 - 1,4 |
| M16 | 17,4 - 17,00 | 30,0 - 29,5 | 3,3 - 2,7 | 2,2 - 1,8 |
| M20 | 21,5 - 21,0 | 37,0 - 36,2 | 3,3 - 2,7 | 2,2 - 1,8 |
| M24 | 25,5 - 25,0 | 44,0 - 43,2 | 4,3 - 3,7 | 2,7 - 2,3 |
| M30 | 31,6 - 31,0 | 56,0 - 55,0 | 4,3 - 3,7 | 2,7 - 2,3 |
| M36 | 37,6 - 37,0 | 66,0 - 65,0 | 5,6 - 4,4 | 3,3 - 2,7 |
Black Washers are dimensioned in BS4320: 1968
| Nominal | Washer Diameter | Washer Thickness | ||
| Size | Internal max - min |
External max - min |
Thickness max - min |
|
| M5 | 5,8 - 5,5 | 10,0 - 9,2 | 1,2 - 0,8 | |
| M6 | 7,0 - 6,6 | 12,5 - 11,7 | 1,9 - 1,3 | |
| M8 | 9,4 - 9,0 | 17,0 - 16,2 | 1,9 - 1,3 | |
| M10 | 11,5 - 11,0 | 21,0 - 20,2 | 2,3 - 1,7 | |
| M12 | 14,5 - 14,0 | 24,0 - 23,2 | 2,8 - 2,2 | |
| M16 | 18,5 - 18,00 | 30,0 - 29,2 | 3,6 - 2,4 | |
| M20 | 22,6 - 22,0 | 37,0 - 35,8 | 3,6 - 2,4 | |
| M24 | 26,6 - 26,0 | 44,0 - 42,8 | 4,6 - 3,4 | |
| M30 | 33,8 - 33,0 | 56,0 - 54,5 | 4,6 - 3,4 | |
| M36 | 39,8 - 39,0 | 66,0 - 64,5 | 6,0 - 4,0 | |
| M42 | 45,8 - 45,0 | 78,0 - 76,5 | 8,2 - 5,8 | |
| M48 | 53,0 - 52,0 | 92,0 -90,0 | 9,2 - 6,8 | |
For DIN125 Plain Washers (Overall dimensions) Din 125 Washer