The minimum thread length is calculated strictly according to EN 14399-3 for preload bolts – System HR and EN 14399-7 for preload countersunk head bolts – System HR.

In calculation, you need to consider standard reference thread length (b), minimum length of the shank – un-threaded part of the bolt, and distance from head  of the bolt till first full thread.

To help with that, we have created two useful calculators:

• Thread Length Calculator for HR Bolts to EN 14399-3
• Thread Length Calculator for HR Countersunk Bolts to EN 14399-7

In any doubts, please contact our Quality Department.