| Screw Thread d | M5 | M6 | M8 | M10 | M12 | M14 | M16 | M20 | ||||
| P | Pitch | Coarse thread | 0.8 | 1 | 1.25 | 1.5 | 1.75 | 2 | 2 | 2.5 | ||
| Fine thread-1 | / | / | 1 | 1.25 | 1.5 | 1.5 | 1.5 | 1.5 | ||||
| Fine thread-2 | / | / | / | 1 | 1.25 | / | / | / | ||||
| b | L≤125 | 16 | 18 | 22 | 26 | 30 | 34 | 38 | 46 | |||
| 125＜L≤200 | / | / | 28 | 32 | 36 | 40 | 44 | 52 | ||||
| L＞200 | / | / | / | / | / | / | 57 | 65 | ||||
| c | min | 1 | 1.1 | 1.2 | 1.5 | 1.8 | 2.1 | 2.4 | 3 | |||
| da | Form A | max | 5.7 | 6.8 | 9.2 | 11.2 | 13.7 | 15.7 | 17.7 | 22.4 | ||
| Form B | max | 6.2 | 7.4 | 10 | 12.6 | 15.2 | 17.7 | 20.7 | 25.7 | |||
| dc | max | 11.8 | 14.2 | 18 | 22.3 | 26.6 | 30.5 | 35 | 43 | |||
| ds | max | 5 | 6 | 8 | 10 | 12 | 14 | 16 | 20 | |||
| min | 4.82 | 5.82 | 7.78 | 9.78 | 11.73 | 13.73 | 15.73 | 19.67 | ||||
| du | max | 5.5 | 6.6 | 9 | 11 | 13.5 | 15.5 | 17.5 | 22 | |||
| dw | min | 9.8 | 12.2 | 15.8 | 19.6 | 23.8 | 27.6 | 31.9 | 39.9 | |||
| e | min | 8.71 | 10.95 | 14.26 | 16.5 | 17.62 | 19.86 | 23.15 | 29.87 | |||
| f | max | 1.4 | 2 | 2 | 2 | 3 | 3 | 3 | 4 | |||
| k | max | 5.4 | 6.6 | 8.1 | 9.2 | 11.5 | 12.8 | 14.4 | 17.1 | |||
| k1 | min | 2 | 2.5 | 3.2 | 3.6 | 4.6 | 5.1 | 5.8 | 6.8 | |||
| r1 | min | 0.25 | 0.4 | 0.4 | 0.4 | 0.6 | 0.6 | 0.6 | 0.8 | |||
| r2 | max | 0.3 | 0.4 | 0.5 | 0.6 | 0.7 | 0.9 | 1 | 1.2 | |||
| r3 | min | 0.1 | 0.1 | 0.15 | 0.2 | 0.25 | 0.3 | 0.35 | 0.4 | |||
| r4 | ≈ | 3 | 3.4 | 4.3 | 4.3 | 6.4 | 6.4 | 6.4 | 8.5 | |||
| s | max=nominal size | 8 | 10 | 13 | 15 | 16 | 18 | 21 | 27 | |||
| min | 7.78 | 9.78 | 12.73 | 14.73 | 15.73 | 17.73 | 20.67 | 26.67 | ||||
| t | max | 0.15 | 0.2 | 0.25 | 0.3 | 0.35 | 0.45 | 0.5 | 0.65 | |||
| min | 0.05 | 0.05 | 0.1 | 0.15 | 0.15 | 0.2 | 0.25 | 0.3 | ||||
Why is it hexagonal, not other?
Many people will have such a question, why should the bolt be designed into a hexagonal shape? And not others? Hexagon is the product of compromise between side length and twist angle.
For bolts with odd side length, the two sides of the wrench are not parallel. In addition, in the early days, there were only forked wrenches, and most of the wrench heads were trumpet shaped, so wrenches were not suitable for power generation. In addition, the twist angle is also an important factor to consider. If it is a four corner, the wrench needs to be turned 90 degrees to fix the screws, which is unfavorable for installation in a narrow space; If it is octagonal or decagonal, although the twisting angle becomes smaller, the force is also small, and it is easy to round.
Therefore, hexagon shape is a common choice for bolts.
