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.
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(A comparison between common bolt securing options)