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 length 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