Andrews Fasteners Ltd

AndFast Malaysia SDN BHD

The Fasteners Specialist

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ISO 888: Thread lengths for ISO metric fasteners (bolts)

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 lengthsĀ l <= 0.5d the bolt should be fully threaded.

Typical thread lengths (b) for popular sizes of fasteners

DiameterM12M16M20M22M24M27M30M33M36
l <= 125303846505460667278
125 < l
l <= 200
364452566066727884
l > 2005765697379859197