Your result

Locking Ability




Worker safety


Initial cost


Lifetime cost


SCALE:    0 = Not Applicable.   1 = Unsuitable.   5 = Excellent.

How did we calculate?

Are double nuts effective
against bolt loosening?

The double nut, also known as jam nut, is a friction locking method that uses two separate nuts on top of each other.

Care must be taken during the tightening of the second nut as overtightening will lead to thread stripping or tensile rupture of the bolt. Although the nuts used for this method require little investment, the installation process itself is time-consuming and relies on the skill of the operator. It is also an unreliable locking method that protects poorly against vibration, which means it must be inspected and maintained often – increasing long-term costs. It is particularly ineffective when lubrication of the bolted joint is required.

Scroll down to access the eBook "Why do bolts loosen?"
(A comparison between common bolt securing options)

Which of the many double nut assembly methods do you use?

The biggest challenge for a bolted joint, causing it to lose preload and fail, is spontaneous loosening. Vibrations are everywhere.

What causes loss of preload?

This video shows all 4 nuts rotated loose!
A steep decline in the graph indicates a failure.

This Junker test shows all 4 nuts rotated loose! 

(The Junker test is the most severe vibration test for bolted connections. The bolted joint is exposed to transverse movements underneath the bolt head or nut, while the clamping force is continuously measured.) 
The effectiveness of different locking methods can easily be compared.



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Which bolt locking product should I use?

See how different bolt locking products perform.

What you will find in the eBook:

  • Pros and cons of the different bolt locking methods
  • Evaluation of different products
  • A print-friendly Guidance for Selection, to help you decide which product to use in your applications


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