The Use Of Two Nuts To Lock A Fastener

What is the jam nuts？

 

 

The jam nut does not actually refer to a technique, but instead, it is a reference to a low-profile type of nut, that is often half as tall as the standard nut you are using in your fastener. The main purpose of this smaller nut is much like the name implies to jam the nut that you used in your fastener in place. It is also commonly used in some situations where for some reason the standard nut would be too big to fit.

 

 

 

 

 

 

 

 

 

 

 

 

Understanding self-loosening can oftentimes be half the work that you need to do in order to combat it. There are actually an array of causes that might be responsible for your fasteners loosening on their own over time, however the most common of these is vibration.
Even the slightest vibration can actually contribute to your nut self-loosening as the small movement of the vibration will lead your nut to slowly start rotating. This rotation or self-loosening might not always be visible at first, but over time it could lead to your entire fastener coming undone.
Stress can also be a big reason why your fasteners lose their effectiveness over time. If your fastener is trying to hold together more than its capabilities are, the stress will eventually cause it to deform or might lead to its self-loosening. This is why tightening nuts more than you should is not an effective way of preventing self-loosening.

 

When it comes to using two nuts to prevent self-loosening the first thing that you will need to actually consider is whether the two nuts that you are using have the same width. In cases where you are using two nuts of the same width then the order in which you will use them will essentially become irrelevant.
However, if you are using two nuts that have different widths, then you will immediately need to make a choice on the order in which these nuts will need to be placed. Normally, in such cases, the nut with the thinner width is going to be the nut that you actually tighten on first. This might seem like a departure from the common belief that wants the thicker nut actually tightened first, but it is the method that will make the most sense if you want to ensure the longevity of your project and that your fasteners are going to remain effective over a long period of time.
This is because when the thick nut comes and tightens on top of the thinner nut, some of the load on the threads of the nut will be loosened. By offsetting some of the load you will ensure that the threads will not get slightly damaged or destroyed over time. This can be particularly important because damaged threads will frequently lead to more self-loosening.

 

Another frequent question that is often asked when it comes to the use of two nuts, is whether or not the two nuts need to be tightened more or less than the amount that they would have normally been tightened. Most people will usually believe that the logical answer to this question is that both nuts need to be tightened an equal amount, or rather that both of them need to be tightened to the maximum tightness possible.
However, this could not be further from the truth as the reality is that when both of the nuts are tightened to extremes you will end up putting too much pressure or inadvertently might end up making additional rotations which would once again lead to more pressure and eventually further self-loosening.
How should you tighten the two nuts in this method?
If you want to protect your fastener's longevity by ensuring that you are not putting too much pressure on it, then what you will want to do is start with your first thinner nut, or equal size nut if your two nuts have the same width.
This first nut will need to be tightened somewhere between 25 and 50 percent of the overall tightening torque. Once it has been tightened you are welcome to put the second nut, which should either be thicker or of equal width, on top. This second nut is the one that you will want to tight completely, or rather to its full torque value.
By following this process, you will effectively ensure that some of the load that would have otherwise been up to the thinner nut to carry is now going to be lifted by the thicker nut. This relief of pressure will help your nuts remain tightened for longer periods of time and it will eliminate the chances of them loosening prematurely.

 

 

The two-nut system is one of the most commonly used systems for ensuring that your fasteners are not going to be self-loosening, however, just because it is commonly used does not necessarily mean that it is completely effective.
The reality of the two-nut system is that in fact, it will only work well if the two nuts have been tightened properly. The proper tightening is what will allow them to get jammed together. When it comes to that jamming the first and foremost thing that you will need to remember is to not overtighten the first or the second nut. Remember that the whole purpose of having two nuts is actually relieving some of the pressure of each nut and not ensuring that both of them are tightened to the maximum possible amount.

 

 

 

Put simply, if the second thicker nut is overtightened what will happen is that you will probably cause thread stripping or cause a tensile fracture of the bolt. This type of damage to the bolt will significantly reduce the effectiveness of your fastener, while simultaneously making it more likely that small movements will cause self-loosening.
However, if both of the nuts are tightened properly and there is no significant thread damage caused during the tightening process, then the whole two-nut method becomes a lot more effective and your fasteners are much more likely to hold together your structure, project, or machinery.

 

The jam nuts, while useful to the two-nut method are usually not used on their own to achieve the desired tightening effects. Currently, there is no research to back the idea that two jam nuts would be successful in keeping your structure from self-loosening. This is why it is much better if you stick to using a thinner and thicker nut.
It is also important to remember that thinner nuts are also known to cause partial thread stripping more frequently. This type of stripping will usually mean that there is further self-loosening. This is why when it comes down to it, it is not recommended for you to use two jam nuts in order to keep your fastener from self-loosening.

 

Conclusion:
The two-nut method can be a particularly effective technique for ensuring that your fasteners are going to hold for a long time. It is usually most effective when you use a jam nut and a thicker nut, however, it can also be achieved through the use of two jam nuts. When it comes to the two-nut method ultimately the most important thing will be to ensure that everything has been tightened properly and that there has not been any thread stripping that occurred during the tightening process as that could increase the chances of self-loosening.

 

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