Among the fastening components that influence the assembly accuracy and durability of a product, screws play a particularly important role. Selecting the right screws can prevent play and loosening between parts, significantly reducing the occurrence of defects and trouble. Furthermore, by adopting materials and surface treatments suited to the operating environment, the risk of corrosion and degradation can be lowered, making it possible to maintain quality over the long term. This article, under the theme of “Improving Quality with Screws,” will explain everything from selection points and how to determine the right materials and shapes to practical quality control methods, supporting the optimization of product quality.

Choosing the right screws stabilizes torque management during fastening, suppressing gaps and wear between components. For example, hexagon socket head cap screws and Torx screws feature sockets that are less prone to slipping, making it easy to secure a consistent tightening force even in narrow spaces. Improved fastening accuracy prevents loosening even against mechanical vibrations and repeated loads, directly leading to long-term product reliability and quality improvement.

If common carbon steel products are used without considering the environmental conditions where the screws will be installed, rust and corrosion can progress rapidly, leading to a degradation of the entire product’s performance. By selecting stainless steel for outdoor or high-humidity environments, and screws with nickel plating or PVD coating for areas around equipment where chemicals are present, the risk of corrosion can be significantly reduced. Combining the right materials and surface treatments for the right application is the key to quality improvement.

It is important to comprehensively evaluate not only the initial cost of screws but also the maintenance frequency and the labor required for replacement work. By introducing screws with high wear and corrosion resistance, the replacement cycle can be extended, which in the long run can suppress total costs. Additionally, by adopting standardized high-performance screws in addition to general-purpose parts to streamline inventory management, opportunity losses due to ordering mistakes or delivery delays can also be prevented. As a result, product quality improvement and operational cost optimization can be achieved simultaneously.

Hexagon socket head cap screws have a structure that allows them to be securely tightened from the inside with a socket wrench or a hex key, making them particularly suitable for work in tight spaces. Since their bearing surface is flat, they have a wide contact area with the nut and excellent load distribution, making them ideal for fastening parts where rigidity is important, such as machine frames and equipment stands. They also contribute to quality stabilization because torque is easy to manage.

The Torx (star-shaped) drive has a large contact area between the driver and the screw head, making it resistant to slipping (cam-out). This allows high torque to be transferred efficiently, making it invaluable in situations where delicate fastening force control is required, such as in the assembly of precision instruments and electronic components. It also helps to suppress wear on the driver tip, contributing to improved maintainability.

Low profile screws are designed with a reduced head height, making them suitable for installation in thin members or tight clearances. By using them to fasten components inside equipment or in the thin-walled sections of casings, protrusions can be minimized, preventing interference and visual clutter. Because the head is less conspicuous, it helps maintain the aesthetic quality of the finished product while increasing the design freedom for thinner profiles.

In environments subject to vibration and shock, screw loosening can lead to quality problems and safety risks. Captive screws, which may feature an integrated washer, a special thread shape, or a locking nut function, maintain their fastening force even under vibration. Their introduction in areas with high dynamic loads, such as automotive parts, heavy machinery, and aviation equipment, can be expected to reduce maintenance frequency and suppress trouble.

Screws used in a vacuum environment must minimize gas release (outgassing) and particle contamination. Screws for vacuum use low-outgassing materials such as stainless steel or titanium and employ designs that minimize creep and expansion characteristics. They are essential components for maintaining internal cleanliness and vacuum levels in the assembly of semiconductor manufacturing equipment and vacuum chambers.

Stainless steel screws form a stable oxide film on their surface due to their chromium content, which prevents rust and corrosion. Therefore, they can be used with confidence not only in high-humidity outdoor equipment and water-related machinery but also in medical and food machinery where strict hygiene management is required. They also have excellent heat resistance, so their dimensional changes are small even under harsh temperature conditions, and their ability to maintain fastening force for a long time contributes to quality improvement.

Titanium alloy screws achieve a tensile strength equal to or greater than that of ferrous metals while being as lightweight as aluminum. They are also strong against metal fatigue and corrosion, making them suitable for weight reduction in aerospace components and high-end sports equipment. Furthermore, their high biocompatibility allows them to be widely used in implants and medical devices, achieving both product quality improvement and user safety enhancement.

Aluminum alloy screws are lightweight and have excellent thermal conductivity, making them ideal for the casings and heat-dissipating structural parts of electronic devices. Although their corrosion resistance is inferior to that of stainless steel, their surface hardness and corrosion resistance can be enhanced by applying an anodic oxidation treatment (anodizing). In addition, tool wear during processing is low, and the manufacturing of complex shapes and small-diameter screws is easy, enabling high-precision fastening while keeping costs and delivery times down.

Surface treatment is the key to dramatically improving the corrosion and wear resistance of screws. Zinc plating and nickel plating are excellent in terms of cost performance and are widely used in general industrial machinery and architectural hardware. On the other hand, PVD (Physical Vapor Deposition) and nano-coating technologies improve hardness and lubricity with a thin film of just a few microns, enhancing resistance to wear and chemical agents. They contribute to quality improvement in precision equipment and environments where high reliability is required.

In fastening work, variations among workers can cause quality defects and trouble. Therefore, it is effective to create a standard operating procedure (SOP) that details the part number of the screw to be used, the tightening torque value, the type of tools, and the tightening sequence, and to display it in a visible location at the worksite. By ensuring that everyone can perform the work according to the same procedure through regular education and training, and by managing the revision history of the SOP, the standardization of work quality and traceability can be secured.

Inspection frequency should be set based on process capability (Cpk) and past defect rates, while considering the balance of cost and time. Even in cases where sampling inspection is normally sufficient, if the defect rate exceeds a set value or if initial defects occur after the introduction of a new lot, it is required to immediately switch to 100% inspection and investigate the cause. Additionally, by periodically reviewing inspection results and revising inspection items and thresholds, an optimal inspection system can be maintained.

For screws with special shapes or extremely small sizes that are difficult to check with general-purpose measuring instruments, it is effective to design and manufacture special inspection jigs to improve measurement accuracy. For example, by introducing jigs for torque testing or gauges that can instantly determine the precision of screw threads, inspection time can be shortened and human error reduced. Using special jigs can significantly suppress the risk of non-conforming products flowing to the next process or to the customer, thereby enhancing quality reliability.

An automotive parts manufacturer was using conventional Phillips head screws, but cam-out of the driver frequently occurred during fastening, and the variation in torque greatly affected quality. When they switched to Torx screws, the contact area between the driver and the screw head increased and slipping was suppressed, resulting in a reduction in the standard deviation of tightening torque by about 15%. As a result, the rate of loosening after assembly was halved, and recall risks and rework labor were significantly reduced.

A precision equipment manufacturer, where corrosion due to humidity fluctuations and chemical agents was a problem, adopted products that had a PVD nano-coating applied in addition to standard stainless steel screws. The nano-level uniform thin film protected the surface, suppressing fastening failures due to corrosion to almost zero. As a result, the field failure rate was reduced by about 30% compared to before, contributing to a reduction in maintenance costs and downtime.

Screw selection is the cornerstone of product quality improvement. By choosing the appropriate shapes, materials, and surface treatments, it is possible to stabilize assembly accuracy, ensure environmental resistance, and optimize lifecycle costs. By utilizing shapes suited to the application, such as hexagon socket head cap screws and Torx screws, and selecting materials like stainless steel, titanium alloy, and aluminum alloy with an understanding of their characteristics, the risks of loosening and corrosion can be suppressed. Furthermore, by developing standard operating procedures, an optimal inspection system, and introducing special inspection jigs, process quality can be standardized and the escape of defective products can be prevented.

First, identify the fastening locations in your company’s products and organize the operating environment and load conditions to formulate the specification requirements for the screws. Next, conduct tightening torque tests and corrosion resistance tests with sample products to verify the optimal combination. Based on those results, revise the standard operating procedures and inspection standards, and conduct on-site training. Even after implementation, periodically review the inspection data and on-site feedback to run a PDCA (Plan-Do-Check-Act) cycle and strive for continuous quality improvement.

Conclusion

For inquiries regarding samples or materials, please respond to this email or contact our sales representative!

At Ohta Vietnam, we not only provide ready-made products such as screws and bolts, but also support activities in the manufacturing field such as cutting, inspection, assembly, packaging…
Our equipment list is here

As a “specialized support” for the manufacturing industry in Asia. If you have any related questions, feel free to contact Ohta Vietnam for detailed support!
URL: https://ohtavn.com/en/contact/