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Column
September 11th, 2026

What is the strength classification of screws? Standards and selection criteria that manufacturers should know: On a manufacturing floor, the failure of a single “screw” can destroy the reliability of an entire product and, in some cases, lead to catastrophic accidents. Especially for industrial machinery with high vibration or infrastructure equipment used in harsh environments, selecting the appropriate “Strength Class” is a top priority in design and procurement. In this article, we provide a comprehensive guide for manufacturing executives, procurement managers, and on-site engineers, covering everything from the basics of screw strength classes to essential calculation formulas and the increasingly popular IoT-driven fastening quality management. Furthermore, we will touch upon the procurement environment in Vietnam, where industrialization is rapidly progressing, and introduce how Ohta Vietnam’s solutions balance cost optimization with quality assurance. We hope this article serves as a guide for safe and efficient fastening design. Numbers such as “4.8” or “10.9” marked on screw heads or packaging represent the “Strength Class.” These numbers serve as a global language indicating how much load the screw can withstand. For example, in the notation “10.9,” the first number “10” indicates the Nominal Tensile Strength, meaning it can withstand up to 1,000 N/mm². The following “.9” indicates that the Yield Point (or proof stress) is 90% of the tensile strength. In other words, if a load of 900 N/mm² or more is applied, the screw will undergo “permanent deformation” and will not return to its original shape. Fastening with over-specified parts without this knowledge leads to increased costs, while under-specified parts significantly increase the risk of breakage. While the Japanese Industrial Standards (JIS) are widely referenced in many manufacturing sites today, most are compliant with the international standard ISO 898-1. In today’s world of global supply chains, understanding these international standards is essential. Particularly when procuring parts from overseas hubs like Vietnam, verifying that quality control is based on JIS or ISO—rather than just local standards—is the key to maintaining “Japanese Quality.” At Ohta Vietnam, we handle only products that strictly comply with these international standards, accurately bringing Japanese design intent to life. The most important factor in screw selection is controlling the “axial force” (the clamping force). To achieve proper fastening, the following basic formula is used: $$T = K \cdot d \cdot F$$ Here, $T$ represents the tightening torque (N·m), $K$ is the torque coefficient, $d$ is the nominal diameter of the screw (mm), and $F$ is the axial force (N). Since the torque coefficient $K$ ...

Column
September 10th, 2026

Mechanisms and solutions for galvanic corrosion of dissimilar metals (electrolytic corrosion): Guide to selecting optimal screws for procurement in Vietnam: In manufacturing, ensuring long-term product life and reliability is an eternal challenge. Particularly in high-temperature, high-humidity environments like Vietnam, metal parts can corrode much faster than expected, potentially leading to fatal product defects. Among these risks, “Dissimilar Metal Contact Corrosion” (Galvanic Corrosion, commonly known as electrolytic corrosion), which occurs when different types of metals come into contact, is a risk often overlooked during the design stage. This article provides a thorough explanation of the scientific mechanisms behind dissimilar metal contact corrosion, practical knowledge of potential differences, and anti-corrosion measures recommended by Ota Vietnam. By reading this article, you will gain specific guidelines to minimize recall risks due to incorrect fastening component selection and establish a cost-effective procurement strategy. Dissimilar metal contact corrosion refers to a phenomenon where, in an environment containing an electrolyte solution (such as moisture or rainwater), different types of metals come into contact, causing an electric current to flow due to the difference in “corrosion potential (ionization tendency)” between them. This results in the metal with the lower potential (the anode) corroding severely. In essence, it is a state where a “battery” is unintentionally formed. For example, if a stainless steel plate is fixed with aluminum screws, the aluminum side will corrode rapidly because its potential is lower, acting as a “sacrificial” metal. This phenomenon can progress several to dozens of times faster than simple oxidation, making it feared as a “silent killer” in the manufacturing industry. For electrolytic corrosion to occur, the following three conditions must be met simultaneously: Contact of Dissimilar Metals: Two or more different metals must be electrically connected. Presence of an Electrolyte: A conductive liquid, such as water droplets, moisture, or salt, must be present at the contact area. Potential Difference: There must be a clear difference in corrosion potential between the metals in contact (generally 0.1V to 0.25V or more). In Vietnam’s factory environments, where average humidity often exceeds 80%, the “presence of an electrolyte” is a constant reality. Therefore, stricter measures are required compared to those used in Japan. When designers select screws, the most important indicator is the “corrosion potential.” Every metal has its own specific potential, and the greater the difference, the stronger the corrosion energy becomes. Key Data: Statistics on Metal Corrosion Potential and Corrosion Rates Potential difference between stainless steel (SUS304) and aluminum alloy: approx. 0.50V to 0.60V (extremely dangerous range) Potential difference between galvanized steel ...

Column
August 31st, 2026

5 Key Indicators for Supplier Evaluation: How to Stabilize Quality, Price, and Delivery: In modern manufacturing, supplier evaluation is an indispensable element for maintaining and enhancing a company’s competitiveness. As global supply chains become increasingly complex, risks related to quality, cost, and delivery are continuously growing. Notably, Vietnam’s manufacturing industry has experienced remarkable growth in recent years, with its manufacturing GDP growth rate reaching approximately 6.9% in 2023 (General Statistics Office of Vietnam). Amidst this boom, selecting and developing local suppliers is a critical challenge for Japanese manufacturing sites to meet the demands for high quality, low cost, and stable supply. Supply chain disruptions can potentially lead to losses of several hundred million yen annually for companies, and increased costs due to defective products are estimated to account for 5-10% of manufacturing costs (Ministry of Economy, Trade and Industry). To mitigate such risks and build a resilient supply chain, an objective and multifaceted evaluation is required for all suppliers, including those providing critical components like fasteners. Ohta Vietnam leverages its extensive experience and local network to support clients in building stable supply chains. In supplier evaluation, “quality” is the most fundamental aspect. Product quality directly impacts the performance, safety, and brand image of the final product, leaving no room for compromise. Especially for fasteners, strict control over dimensional accuracy (e.g., within ±0.05mm), material, and surface treatment is essential. Product Quality: Evaluate accuracy, functionality, and durability as per drawings. The target defect rate should aim for 100 ppm (Parts Per Million) or less. Process Quality: Standardization of manufacturing processes, process control, and establishment of inspection systems are crucial. Verify the presence and operational status of certifications such as ISO 9001 (international standard for quality management systems), with over 80% of key suppliers ideally holding such certifications. Aim for an inspection pass rate of 99.5% or higher. Commitment to Quality Improvement: Assess the proactiveness in root cause analysis and recurrence prevention measures for defects, as well as continuous improvement activities (Kaizen). Efforts to keep the number of customer complaints below X per year are expected. Fostering a quality culture among Vietnamese suppliers is vital for bridging the gap with the high-quality standards demanded by Japanese companies. Ohta Vietnam provides support in closing this gap through quality audits and technical guidance for local suppliers. Alongside quality, “price” significantly influences a company’s competitiveness. It is crucial to select suppliers who not only offer competitive pricing but also demonstrate transparent cost structures and continuous efforts toward cost reduction. ...

Column
August 28th, 2026

Screw Supply Chain Design for Emergency Procurement: Practical Strategies to Reduce Shortage Risks: In recent years, global supply chain disruptions have severely impacted the manufacturing industry, with approximately 70% of manufacturers experiencing production halts or delays in a 2021 survey. Strengthening supply chain resilience is an urgent imperative. Screws, indispensable for product assembly, can bring an entire production line to a standstill if even a single unit is missing, leading to losses ranging from tens of millions to hundreds of millions of Japanese Yen per day. Since the pandemic, there have been reports of component procurement costs increasing by an average of 15% due to soaring logistics costs and fluctuating raw material prices. Manufacturers must redesign robust supply chains to prepare for emergency procurement. This represents a strategic investment at the core of any Business Continuity Plan (BCP). This article will delve into practical supply chain design strategies to minimize screw shortage risks and ensure responsiveness during emergencies. Ohta Vietnam leverages its extensive experience and local network in Vietnam to strongly support clients in strengthening their screw supply chains. We provide concrete solutions to maximize the potential of local procurement in Vietnam, ensuring stable component supply and cost optimization. Screw supply chains are exposed to numerous risk factors. External environmental factors such as geopolitical risks, natural disasters, and pandemics have profoundly impacted supplier production capabilities and logistics networks, exposing supply chain vulnerabilities. Fluctuations in raw material prices also pose a significant challenge. The prices of steel and stainless steel, key raw materials for screws, are highly susceptible to international supply-demand dynamics and exchange rates. Historically, cases of annual price fluctuations of up to 30% have been observed. Logistics stagnation and soaring transportation costs also exert pressure. In international shipping, port congestion, container shortages, and rising fuel costs have combined to cause sea freight costs to temporarily surge by more than five times during certain periods. Extended procurement lead times and increased costs are inevitable. Over-reliance on specific suppliers, known as single-source risk, represents the most vulnerable point in a supply chain. Depending on a sole supplier carries the risk of complete production stoppage should issues arise. Vietnamese manufacturing faces similar challenges. While experiencing rapid growth, it heavily relies on overseas component procurement, with an estimated foreign dependency of approximately 60-70%. High-precision and specialized screws, in particular, are currently imported. This high foreign dependency exacerbates vulnerabilities during supply chain disruptions, making the promotion of local procurement a crucial strategy for risk reduction and resilience. ...

Column
August 21st, 2026

Vietnam vs. Japan Procurement Comparison: What is the Optimal Hybrid Strategy?: The manufacturing landscape has become increasingly complex and uncertain, exacerbated by geopolitical risks, currency fluctuations, soaring raw material and labor costs, and recent supply chain disruptions due to pandemics and international conflicts. Ensuring stable supply and maintaining cost competitiveness are urgent priorities. As the risks of relying on a single source of procurement grow, the importance of a ‘hybrid procurement strategy’ has never been higher. This strategic approach aims to strengthen overall supply chain resilience, enable flexible responses to market fluctuations, and achieve sustainable business growth. This article provides a comparative analysis of the procurement environments in Japan, known for its high quality and reliability, and Vietnam, recognized for its cost competitiveness and growth potential. We will delve into the types, benefits, challenges, and countermeasures for successful optimal hybrid strategies that leverage the strengths of both countries to support sustainable growth. We will provide practical explanations using the procurement of fastening components (such as bolts, nuts, and screws used to secure mechanical parts) as an example. Ohta Vietnam leverages its extensive experience and network in Vietnam to strongly support our clients in optimizing their supply chains. We hope this article will assist you in re-evaluating your procurement strategies. Understanding the characteristics of each country’s procurement environment is essential for an optimal hybrid strategy. Japan’s manufacturing industry boasts world-class quality and reliability. Its precision machining technology enables the production of components requiring micron-level accuracy across diverse sectors, including automotive parts, medical devices, and aerospace. A skilled workforce, with advanced techniques and quality consciousness cultivated through years of experience and On-the-Job Training (OJT), supports stable production. Advantages: High Quality and Reliability: Strict quality standards compliant with JIS (Japanese Industrial Standards) and advanced technical capabilities. Precision Machining Technology: Manufacturing of components requiring micron-level accuracy. Skilled Workforce: Stable production supported by experienced technicians. Quick Lead Time Capability: Rapid development and production through collaboration with domestic suppliers. Strong Supplier Relationships: Trust and technical cooperation fostered through long-term partnerships. Disadvantages: High Labor Costs: The average monthly wage in manufacturing is around 300,000 JPY (as of 2023), which is high. Total labor costs further increase when social security and benefits are included. Soaring Raw Material Costs: Highly susceptible to international market price fluctuations, and also vulnerable to the impact of a weaker yen due to reliance on imported raw materials. Labor Shortage: The decline in skilled workers due to the aging population and low birthrate is severe, ...

Column
August 14th, 2026

Quality Assurance System for Screw Procurement in Vietnam: Inspection, Certification, and Traceability: Vietnam, with its robust economic growth and abundant workforce, has become a crucial hub for global manufacturing. Over the past five years, the manufacturing GDP growth rate has averaged over 6% annually. More than 2,000 Japanese manufacturing companies have established operations here, driven by objectives such as relocating production bases and diversifying supply chains, and this number continues to rise. However, amidst this growth, quality assurance for component procurement, especially for fastening parts like screws, presents an urgent challenge for Japanese companies. Screws are critical components directly impacting product safety, durability, and functionality, ultimately determining the quality of the final product. It is estimated that a 1% defect rate in screws can account for 3% of total production costs, indicating that quality issues can lead to increased costs and brand damage risks. This article clarifies the quality challenges in screw procurement in Vietnam and explains concrete methods for establishing a quality assurance system to overcome them. Ensuring a rigorous inspection system, reliable quality certificates, and robust traceability (manufacturing history tracking) are key to stable screw procurement. While Vietnam’s manufacturing industry is developing rapidly, the supplier market for basic components like screws is diverse, with varying quality levels. There are an estimated 200+ screw suppliers domestically, but many are small and medium-sized enterprises (SMEs) with often underdeveloped manufacturing facilities and quality control systems. In fact, SMEs account for approximately 97% of Vietnam’s manufacturing sector, making the selection of high-quality suppliers challenging. The main quality challenges for Japanese companies procuring screws in Vietnam are as follows: Gap with Japanese Standards: The quality consciousness, stringent inspection systems, and high technical levels demanded by Japanese companies can be a significant hurdle for many local Vietnamese suppliers. Discrepancies between Japanese and local standards are particularly common in dimensional accuracy, material uniformity, and surface treatment quality. Risk of Counterfeit and Substandard Products: In a market with strong cost-reduction pressures, there is a risk of inexpensive counterfeit or substandard products circulating. These can be difficult to distinguish visually and may compromise product reliability due to insufficient material strength or improper surface treatment. Recall costs due to quality issues have been reported to range from several hundred million to several billion JPY on average, depending on the industry and product. Balance Between Cost Reduction Pressure and Quality Maintenance: One of the biggest attractions of procurement in Vietnam is cost reduction. However, excessive cost-cutting pressure carries the risk of ...

Column
August 07th, 2026

Quotation Comparison and Order Management to Avoid Mistakes in Small-Lot, High-Mix Screw Procurement.: In modern manufacturing, the diversification of customer needs and the shortening of product lifecycles are accelerating multi-variety, small-lot production. This trend significantly impacts the procurement of fastening components, especially “screws,” which constitute products. Procuring a wide variety of screws, from standard items to specialized specifications, in small quantities and in a timely manner, has become a complex challenge for many companies. While the procurement cost of fastening components typically accounts for a small percentage, ranging from 1% to 5% of the total product cost, the man-hours required for their management are by no means negligible. In fact, one survey reported that approximately 30% of procurement personnel spend a significant amount of time on supplier sourcing and quote comparison. These diverse challenges—cost, quality, delivery time, and management man-hours—can increase the workload of procurement staff, leading to decreased production efficiency and unforeseen risks. This article will explain specific quote comparison methods and key points for efficient order management to ensure successful small-lot, multi-variety screw procurement. Furthermore, it will discuss how Ohta Vietnam, with its strengths in procurement in Vietnam, can contribute to solving your company’s procurement challenges. Our aim is to support the enhancement of your manufacturing site’s competitiveness through appropriate strategies and partnerships. Due to its nature, small-lot, multi-variety screw procurement entails numerous unique challenges and risks. Understanding these challenges is the first step towards implementing effective countermeasures. Finding suppliers capable of handling specialized specifications and small-lot production is not easy. The market contains tens of thousands of screw types, with JIS standard products alone numbering in the thousands. Locating a supplier that meets specific needs can take an average of 10 to 20 hours per case. Furthermore, the process of comprehensively evaluating quality, technical capabilities, and responsiveness to select a reliable supplier places a significant burden on procurement personnel. The unit price of screws in small-lot production tends to be 20% to 50% higher compared to large-lot production. This is due to factors such as reduced production efficiency and setup changeover costs on the supplier’s side. Additionally, multiple factors beyond the component unit price, such as tooling costs, transportation fees, exchange rate fluctuations, and payment terms, complicate quote acquisition and price negotiation. When comparing quotes from multiple suppliers, it is essential to evaluate these elements comprehensively. Increased product variety makes it difficult to expand quality control items and standardize inspection criteria. The defect rate for fastening components can average several ...

Column
July 24th, 2026

Proper Maintenance Methods for Stainless Steel Screws and Tips for Extending Their Service Life: “It is stainless steel, so it should not rust”—in manufacturing sites, this misconception ceaselessly invites unexpected troubles and increased costs. Certainly, Stainless Steel possesses excellent corrosion resistance, but in high-temperature, high-humidity environments like Vietnam, or under improper maintenance, corrosion and “galling” occur, directly linking to serious risks such as production line stoppages and product recalls. Particularly in the Vietnam market, where precision equipment and automotive parts manufacturing are accumulated, the reliability of fastening parts is a lifeline that determines the brand value of the final product. In this article, based on the specialized knowledge of fastening parts that Ohta Vietnam has cultivated over many years, we will scientifically reaffirm the characteristics of stainless steel screws and explain correct maintenance methods and secrets for extending service life that can be immediately practiced on-site. We present a concrete roadmap to realize significant reductions in procurement costs and downtime by reducing part replacement frequency through appropriate management. This series of knowledge should become a beneficial asset for all manufacturing industry stakeholders, from management layers to on-site technical personnel. First, let us share the technical basics. The reason stainless steel is hard to rust is that the contained chromium (Cr) bonds with oxygen to form a dense protective film called a “Passive Film” on the surface. The thickness of this film is merely 1 to 3 nanometers (1 nanometer is one-millionth of a millimeter), which is extremely thin, but it possesses a self-repairing function. However, this self-repairing function is not all-powerful. Even with SUS304 (18Cr-8Ni) defined by standards such as JIS G 4303, if iron powder adheres to the surface (“contact rust”) or in the presence of chloride ions (seawater or salty breeze), the film is destroyed, regeneration cannot keep up, and corrosion progresses. In particular, chlorine ions locally destroy the passive film and become the main cause of deep hole-like rust called Pitting Corrosion. Vietnam’s average humidity exceeds approximately 80% throughout the year, and can reach nearly 90% during the rainy season. This high humidity makes it easy for a moisture film to form on metal surfaces, promoting electrochemical corrosion reactions. Furthermore, accompanying rapid industrialization, the atmosphere in factory zones may contain sulfur oxides (SOx) and nitrogen oxides (NOx); these react with moisture to create an acidic environment, becoming factors that accelerate the corrosion of stainless steel screws. Even stainless steel screws that can be expected to have a durability of over 30 ...

Column
July 17th, 2026

5 ways to prevent screws from loosening that you should know at the manufacturing site: In the manufacturing industry, the risk of a single “screw loosening” causing a serious accident or recall is one of the issues that top management and site managers should be most vigilant about. In fact, according to a cause investigation of screw fastening-related troubles (1977 domestic survey in Japan), tightening defects account for about 43% and loosening accounts for about 20%, and it is considered highly probable that these can be prevented with appropriate knowledge and management. Especially in overseas production bases like Vietnam, environmental factors different from Japan (temperature, humidity, vibration) and quality variations in procured parts amplify the risk of loosening. Overconfidence that “it’s fine because I tightened it with the usual torque” can lead to unexpected line stoppages and increased costs. In this article, for technical staff and procurement managers at manufacturing sites, we will explain “5 loosening countermeasures” that can be implemented immediately, while scientifically unraveling the mechanism of screw loosening. Furthermore, we will touch upon stable procurement in Vietnam and the latest axial force management utilizing IoT, presenting concrete action plans to protect factory safety and productivity. Screw loosening is broadly classified into “loosening accompanied by rotation” and “loosening not accompanied by rotation.” What is frequently overlooked on site is “initial loosening (initial settling),” which is not accompanied by rotation. Immediately after tightening a screw, minute irregularities on the bearing surface of the bolt, the screw threads, and the contact surface of the clamped material are crushed and smoothed by the external load. As a result, the contact surface sinks at a micro level (plastic deformation), and the bolt tension (axial force) decreases. Generally, it is said that the axial force immediately after tightening decreases by several percent to about 10% within a few hours to a few days, and design and retightening considering this are necessary. More serious is “return rotation” caused by vibration or impact. When the frictional force acting between the bolt and nut is momentarily lost due to lateral cyclic loading (such as Junker vibration), the screw begins to rotate in the loosening direction naturally along its own lead angle. Once rotation begins, the axial force rapidly approaches zero, leading to falling off or breakage in the worst case. From here, we will introduce 5 specific countermeasures to consider at manufacturing sites from the viewpoints of cost, workability, and reliability. The basic and ultimate secret of loosening countermeasures is to apply ...

Column
July 10th, 2026

What is a stud bolt? ｜Easy explanation in 3 minutes: In manufacturing sites and plant designs, “Stud Bolts” are indispensable as unsung heroes. Unlike general hexagon bolts, this bolt has the unique shape of “having no head.” Why is it frequently used in flange connections for automotive engines and chemical plants? In conclusion, the biggest reasons for adopting stud bolts are “protection of the base material’s threads” and “ease of repeated disassembly and assembly”. They demonstrate their true value especially in locations requiring frequent maintenance or when fastening with base materials of relatively lower strength, such as aluminum die-cast. In this article, we will explain important points that procurement and technical personnel should know in 3 minutes, ranging from basic knowledge of stud bolts and how to read strength classes based on JIS standards, to procurement strategies in Vietnam which is a key card for cost reduction. We will also present hints to solve your company’s procurement challenges while incorporating the merits of local procurement provided by Ohta Vietnam. A Stud Bolt refers to a “rod-shaped bolt threaded at both ends and having no head”. Generally, it takes a structure where one side is embedded into the base material (engine block or equipment body) and a nut is attached to the other side for tightening. In JIS standards (Japanese Industrial Standards), it is classified as a “stud,” and broadly divided into the following types based on shape. Double end (Type with an implant side and a nut side): It is divided into the side screwed into the base material (implant side) and the side where the nut is tightened (nut side). Full thread (All-thread type): A type where the entire shaft is threaded, mainly used for flange connections, etc. Due to this shape, stud bolts also serve as “positioning guides.” When installing heavy flanges or covers, by planting the stud bolts first, parts can be temporarily placed by passing them through the bolts, significantly improving work efficiency. When compared to hexagon bolts, stud bolts have clear engineering merits. Reduced damage to base material: Repeating attachment and detachment with hexagon bolts wears down the female threads of the base material (especially aluminum or cast iron), and in the worst case, the threads get crushed. With stud bolts, since the base material side remains fixed and only the nut side is operated, expensive component bodies are not damaged. Securing strong axial force: Since it is tightened with nuts from both sides (or ...