In the industrial world, the idea is still widespread that, when in doubt, choosing a “larger”, “stronger” or “more robust” fastening element is always the safest option. It is an understandable approach: oversizing seems to offer a margin of reassurance and reduce the risk of failure.
In reality, in fastening, this logic can prove counterproductive. An apparently cautious choice can introduce hidden problems that compromise joint reliability, increase costs, and make the process less controllable.
Why Oversizing Is a Mental Shortcut
Oversizing often arises as a quick response to uncertainty. When precise data are missing, when the application context has not been analyzed in depth, or when time is short, increasing dimensions and strength seems like a simple solution.
This mental shortcut, however, shifts the problem instead of solving it. Without a systemic assessment, oversizing does not eliminate critical variables, but temporarily masks them.
Real Loads and Joint Behavior
A threaded joint does not work only according to the nominal strength of the screw. Its behavior depends on preload, the stiffness of the connected components, and the distribution of loads in service.
Oversizing the screw can alter this balance. A stiffer screw (that is, a screw that elongates less under load, typically because it has a larger diameter or a reduced clamped length), combined with less stiff components, can reduce the joint’s ability to absorb load variations, making it more sensitive to vibrations and cyclic stresses.
In these cases, increasing the resistant section does not automatically translate into greater safety.
The Risk of Overload and Damage
Another often underestimated effect concerns tightening. Screws of larger dimensions or higher strength classes require higher torques to achieve the correct preload.
If the tightening process is not properly controlled, the risk is exceeding the limits of the connected components, causing permanent deformation, surface damage, or local yielding.
In these cases, the joint fails not because of insufficient strength, but because of excessive stress.
Effects on Repeatability and Process Control
Oversizing also introduces further critical issues from the standpoint of the production process. Larger or stronger fastening elements amplify sensitivity to tightening variables, increasing the dispersion of results.
This makes it more difficult to achieve adequate repeatability and reduces the effectiveness of downstream controls. Once again, a choice made to “play it safe” can make the process less stable and harder to manage.
Hidden Costs and Unnecessary Complexity
Beyond the technical aspects, oversizing involves costs that are often invisible. Larger fastening elements affect:
higher unit costs,
longer assembly times,
different tools and equipment,
an increase in the number of variants managed.
When these choices are not guided by clear criteria, complexity grows without delivering real benefits in terms of reliability.
When Oversizing Becomes a Risk
Oversizing becomes particularly critical when it is used as a substitute for analysis. In these cases, the real behavior of the joint is not understood, and reliance is placed on a safety margin that is only apparent.
A correct choice, instead, comes from understanding loads, operating conditions, and the behavior of the fastening system as a whole.
The Contribution of VIPA Academy
Addressing the topic of oversizing means encouraging a more mature reflection on fastening choices. VIPA Academy offers technical content that helps interpret fastening as a system, highlighting the limits of “abundant” solutions when they are not supported by clear criteria.
Promoting a shared technical culture makes it possible to reduce recurring errors, improve the predictability of joints, and make decisions more informed.
Conclusion
In fastening, “larger” or “stronger” does not automatically mean “safer”. Oversizing can introduce hidden risks that compromise the overall reliability of the joint and of the production process.
Only an approach based on understanding the application context and controlling the variables makes it possible to achieve truly reliable results.
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 – Fastening elements and application criteria
Technical references available in the VIPA Catalogue (current edition)
