Calculation of thread lengths
Typical, unless specified in a product standard, dimensions for thread lengths (b) is calculated as follow:
- for l <= 125 mm: b = 2d + 6mm
- for 125 mm < l <= 200 mm: b = 2d + 12mm
- for l > 200mm: b = 2d + 25mm
Where l is lenght of the bolt and b is the threaded part of the bolt.
For bolt, where lengths l <= 0.5d the bolt should be fully threaded.
Typical thread lengths (b) for popular sizes of fasteners
| Diameter | M12 | M16 | M20 | M22 | M24 | M27 | M30 | M33 | M36 |
| l <= 125 | 30 | 38 | 46 | 50 | 54 | 60 | 66 | 72 | 78 |
| 125 < l l <= 200 | 36 | 44 | 52 | 56 | 60 | 66 | 72 | 78 | 84 |
| l > 200 | – | 57 | 65 | 69 | 73 | 79 | 85 | 91 | 97 |