What is the minimum thread length on preload bolts?

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 the head of the bolt till first full thread.

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

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