If two nuts are desired to be used, for whatever reason, use of two normal height nuts would avoid the thread stripping issue. The two videos shown below presents the results of a Junker fastener vibration test performed on the two arrangements that a thick and thin nut on can be arranged.

Typically only one washer is used on the side with the nut. It distributes the pressure more evenly and provides a flat surface so the nut won’t come loose. You can use one on the bolt side as well if the surface is particularly rough or uneven, and that’ll help. Washers are not to be used as spacers though.

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.

Jul 1, 2009 · The mechanisms of loosening-resistance components are investigated within the framework of the three-dimensional finite element method (FEM). In this paper, we have evaluated the ability of double-nut tightening method (DN) and spring washer (SW) to resist self-loosening due to transverse loading.

Oct 11, 2023 · Is there any benefit to using both a double nut and a washer to ensure a nut doesn't lose itself? Or is it just best to use one or the other?

Jan 11, 2015 · Double Nutted joints with jam nuts are affected by order of clamping. While I’m talking about bolt locking techniques, I’ll share another interesting one: For double nut connections involving the use of a jam nut & a standard nut, it REALLY matters what order you install them in. The jam nut should go on first!

Oct 16, 2023 · I was told by a senior that a spring lock washer with double nuts can be used to prevent loosening by vibration. Is this correct? If not, what would be a good application of a double nut + helical spring washer?

Feb 24, 2018 · RCSC Section 6 tells you everything you need to know about washers. There's no impact on capacity, but they are definitely required under the head in certain circumstances.

Feb 1, 2022 · The third category is the frictional locking installation, which achieves anti-loosening performance by increasing the frictional forces between internal and external threads, or between bearing surface and nut (or bolt head), such as double nut and spring washer.

Double nuts are more reliable than other standard nuts because they secure components in scenarios where single nuts are ineffective. In some applications, failure in fasteners leads to serious issues.