Andrews Fasteners Ltd

AndFast Malaysia SDN BHD

The Fasteners Specialist

+44 (0) 113 246 9992

Andrews Fasteners Bolt length (HR) Calculator

Andrews Fasteners Bolt Length Calculator

EN 14399 Pre-load bolt assemblies (HR)

HR Bolt to EN 14399-3:2015 / HR Countersunk bolt EN 14399-7:2007

This calculator is for guidance only and is used for calculating the minimum recommended  bolt length based on maximum allowed thickness of the assembly components and the steelwork.

This information is provided in good faith and is for your guidance only. Andrews Fasteners Limited / AndFast Malaysia cannot accept any liability for actions taken by third parties based on this information.


Bolt diameter M (12 for M12 etc. - up to 36 for M36)
Steelwork thickness (thickness in mm)
No of Washers (Part 5 or/and Part 6) (typically blank = 0, 1 or 2)
DTI Washer (Part 9) (typically blank = 0, or 1)
BFW (Part 9) (typically blank = 0, or 1)
NFW (Part 9) (typically blank = 0, or 1)

Bolt length (calculated)
Bolt length X (ref.) (mm)
Version: 1.02.261118.14399.2015

Nut used in calculation refer to EN 14399-3 / EN 14399-7 (HR Nut)

Washer refer to EN 14399-5 (4) (washer under the nut) or EN 14399-6 (4) (chamfered washer under bolt head) – Hardness 300-370 HV

NFW (2) refers to Nut Face Washer EN 14399-9 (Hard washer) – Hardness 38-45 HRC

BFW (2) refers to Bolt Face Washer EN 14399-9 (Hard washer) – Hardness 38-45 HRC

DTI (1) refers to Direct Tension Indicators Washer EN 14399-9 – Hardness max. 380 HV – maximum height including protrusions (3).

Steelwork refers to the thickness of the steelwork that needs to be tightened including minimum 1 thread above the face of the unloaded nut on the assembly. If additional plates are required Рi.e. to cover oversized holes Рinclude thickness into total thickness of the steelwork.

Short link:

For calculation of thread length refer to: