Introduction
In the industrial world, it is common to attribute a fastening issue to the component being used. When a joint loosens, breaks, or fails to deliver the expected performance, the first reaction is to question the screw, nut, or bolt.
In most cases, however, the component is correct. What does not work is the way it is used.
A screw may fully comply with standards, have the appropriate strength class, and be correctly selected during the design phase, yet still fail in service. Understanding why this happens is essential to avoid recurring errors and improve joint reliability.
When the Problem Is Not the Product
In the previous VIPA Academy article on tightening repeatability, we saw how a correct procedure does not automatically guarantee a reliable result if the actual process is not sufficiently controlled.
The same principle applies to fastening components. A “right” screw on paper may fail when used in an application context that does not take all variables into account. In these cases, the problem is not product quality, but an application error.
Analyzing these errors is not about assigning blame, but about gaining awareness of the mechanisms that lead a joint to behave differently from what was expected.
Error 1: Selecting the Screw Without Considering the Real Application
One of the most common mistakes is selecting a fastening element based solely on dimensions and strength class, without evaluating the operating context.
Factors such as dynamic loads, vibrations, thermal cycles, corrosive environments, or frequent assembly and disassembly operations have a decisive impact on joint behavior. A screw that is mechanically correct may prove unsuitable if the application requires specific characteristics that are not considered during selection.
This aspect is closely linked to the concept of fastening as a system, which will be explored in the next Academy articles.
Error 2: Relying on Tightening Torque as the Only Parameter
Another frequent cause of problems is using tightening torque as the sole operational reference. As previously discussed (read the article here), torque is a direct parameter that does not always directly correspond to the applied load.
Assuming that meeting a torque value is sufficient to guarantee proper preload means ignoring the real variability of the process. The result may be an underloaded or overloaded joint—both conditions that increase the risk of failure.
In these cases, the screw does not fail because it is inadequate, but because the tightening method is not aligned with the required level of reliability.
Error 3: Underestimating the Influence of Auxiliary Components
Washers, bearing surfaces, and mating components are often considered secondary elements. In reality, they play a decisive role in load distribution and joint stability.
Low-quality washers, non-flat surfaces, or materials with significantly different stiffness can alter joint behavior even when the screw itself is correct. Once again, the failure is not attributable to the single fastening element, but to the entire system of components involved.
Error 4: Ignoring Assembly Process Variability
Even when a procedure is defined, the assembly process introduces variability. Uncalibrated tools, different working methods between operators, or changing environmental conditions all affect the final result.
When these aspects are not taken into account, the issue is often interpreted as a product defect, whereas in reality the process is not sufficiently controlled.
This is one of the reasons why two joints made with the same screw can behave very differently over time.
Error 5: Lack of Consistency and Standardization
Another widespread mistake is using different solutions for similar applications. The absence of standardization increases the number of variables and makes it more difficult to identify the causes of potential issues.
The presence of multiple fastening variants, finishes, and supply sources—if not governed by clear criteria—introduces unnecessary complexity and reduces the overall stability of the assembly process.
Why These Errors Lead to Failure
Application errors rarely result in immediate failure. More often, they create borderline conditions that, over time, lead to loss of preload, loosening, or progressive damage.
In these cases, the screw is not “wrong” in absolute terms, but used outside a coherent context. Understanding this dynamic makes it possible to shift the focus from the single component to how it is used.
The Contribution of VIPA Academy
VIPA Academy addresses these topics with the aim of spreading greater technical awareness in the fastening field. Analyzing the most common application errors means providing useful interpretation tools for designers, production managers, and purchasing departments to correctly understand the critical issues that arise during assembly.
Promoting a shared technical culture is the first step toward reducing recurring errors and improving joint stability over time.
Conclusion
When a “right” screw fails, the cause is almost always related to how it is used. Shifting the focus from fastening elements to application conditions allows recurring issues to be prevented and supports more informed technical decisions.
In the next VIPA Academy articles, we will continue exploring how to design and manage fastening as a system, reducing complexity and increasing overall reliability.
Sources and References
ISO 898-1 – Mechanical properties of fasteners made of carbon steel and alloy steel
https://www.iso.org/standard/60610.html
NASA – Fastener Design Manual (RP-1228)
https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf
VIPA Technical Catalogue – Fasteners and application criteria
Technical references available in the VIPA Catalogue (current edition)
