“Screws? Aren’t they all the same?”

That’s what I used to think a few years ago when I first tried DIY. But when I went to buy screws, I was overwhelmed by the sheer variety. In reality, the world of screws is deep, with precise specifications for dimensions and materials defined by standards such as JIS and ISO. This article provides a beginner-friendly explanation of the fundamentals of screws.

Screws are used in furniture, home appliances, automobiles, and many other products around us. Without screws, these products would fall apart. Screws are essential components for fastening and assembling, and standards are crucial to maintain the quality and safety of products. Without standards, screw dimensions and strength would vary, leading to issues during assembly or repair.

JIS (Japanese Industrial Standards) are standards used in Japan, while ISO (International Organization for Standardization) defines global standards. Although JIS references ISO, it has evolved independently to suit Japan’s industrial and technological landscape. Therefore, there are some differences between JIS and ISO screw standards.

JIS (Japanese Industrial Standards) was established to improve the quality and standardization of Japan’s industrial products and to support the development of domestic industries. On the other hand, ISO (International Organization for Standardization) aims to facilitate international trade and promote technological cooperation by establishing common global standards. While JIS is based on ISO, it features unique standards that reflect the specific needs and conditions of Japanese technologies and industries.

The main differences between JIS and ISO screw standards can be seen in aspects such as dimensions, thread pitch, material, and strength. For example, screws with the same nominal diameter may have different pitches in JIS and ISO standards. Additionally, JIS includes some screw types that have been uniquely developed in Japan. When it comes to material and strength, JIS standards are often tailored to suit the environmental conditions within Japan, which may differ from those specified by ISO.

For example, an M3 screw has a pitch of 0.6mm in JIS and 0.5mm in ISO. These differences in pitch mean they are not interchangeable. JIS also includes screws not found in ISO, such as certain small-sized screws. Using diagrams or comparison tables makes these differences easier to understand.

As shown above, the pitches differ between JIS and ISO.

“Huh? This screw doesn’t fit…”

This is a common problem during DIY projects. The cause may lie in the difference in screw standards. Even though JIS and ISO screws may look similar, they generally are not compatible due to differences in dimensions and thread pitch.
In particular, if you try to use an ISO screw on a product designed for an older JIS standard, it may not fasten properly — and that could lead to unexpected failures or accidents.
To ensure compatibility, check the standards chart or consult a specialist.

If you force in an incompatible screw, it can strip the threads or break the screw entirely.
For example, if you insert an ISO screw into a JIS-threaded hole, it might go in at first, but over time, the threads will wear down, causing instability.
In the worst-case scenario, the screw could get stuck and make it difficult or impossible to disassemble or repair the product.
Also, using screws with insufficient strength could lead to structural failure or accidents.
That’s why it’s so important to pay close attention to screw compatibility and always use the correct standard for your application.

“I have no idea which screw to choose…”

Have you ever felt lost in the screw aisle at a hardware store? Screw selection requires careful consideration based on the intended use and environment. For outdoor use, stainless steel screws that resist rust are ideal. For areas with high vibration, use screws with anti-loosening features. Always match material and function to usage conditions.

When selecting screws, you need to consider four main elements:
-Size: Refers to the screw’s diameter and length, which should match the parts you are assembling.
– Pitch: Indicates the spacing between threads. It affects both how tightly the screw holds and how resistant it is to loosening.
– Material: Common materials include steel, stainless steel, and brass. Choose based on environmental factors like moisture, temperature, or corrosion risk.
– Strength: This refers to the load-bearing capacity of the screw and should be selected according to the weight or force applied to the assembled components.
It’s essential to evaluate these factors together to select the most suitable screw for your needs.

There are various types of screws such as metric, unified, and Whitworth. Metric screws use millimeters and are common in Japan and Europe. Unified screws use inches and are standard in the U.S. Whitworth screws, an old British standard, are now rarely used except in old machinery or piping.
Each screw type has unique features and applications. Therefore, it’s important to choose the correct type based on the parts and environment involved.
When in doubt, consult a standard chart or seek advice from a professional to ensure you pick the right one.

“Just tighten it hard, right?”

Actually, that’s a common pitfall. Proper tightening torque is crucial. Torque is the force used to tighten a screw — too much and it breaks; too little and it loosens. Use a torque wrench to apply the correct torque based on the screw’s standard, material, and application. I realized the importance of this when assembling furniture. At first, I thought it was a hassle, but I was amazed by its precision. Proper torque greatly affects durability.

Screws can loosen due to vibration or impact, especially in environments like automobiles or machinery where movement is frequent. In such cases, anti-loosening measures are essential.
There are several solutions:
– Lock nuts: These have special shapes or threads that resist loosening.
– Thread-locking adhesives: These are applied to the screw threads and harden to prevent loosening over time.
Choose the appropriate anti-loosening method based on the usage environment and purpose. For high-vibration settings, applying the correct method is key to safety and reliability.

How to Store Screws Properly
Screws also require proper storage. If stored in humid or extreme temperature environments, they can rust or deform. To prevent this:
– Store them in a dry place, away from moisture.
– Sort them by type and size for easy access.
– Add desiccants (like silica gel) to the storage box to reduce moisture and protect against rust.
Organized and protected screws make your projects more efficient and prevent unexpected delays.

“So, should I choose JIS or ISO?”

When you’re unsure which screw standard to use, the most reliable guideline is to look at the country of origin of the product or component.
– For products and parts manufactured in Japan, screws that follow the JIS standard (Japanese Industrial Standards) are commonly used.
– For overseas products or imports, ISO standard (International Organization for Standardization) screws are typically used.
However, due to the increase in international trade, the use of ISO screws is also becoming more common within Japan. In particular, for products intended for export or those co-developed with international manufacturers, it’s standard practice to adopt ISO screw specifications.

The use of screw standards varies by industry:
– Automotive industry: Given the global supply chains in place, ISO screws are widely used to maintain international compatibility.
– Electronics industry: Many products are designed for domestic use, so JIS screws remain the mainstream. However, products like smartphones and computers, which contain many foreign-made components, often incorporate ISO screws as well.
– Construction industry: Due to local building codes such as the Building Standards Act, JIS screws are generally used. That said, as the use of foreign-made construction materials is increasing, ISO screws are also becoming more prevalent.
In summary, the appropriate standard differs by industry and application. Always check the specifications of the product or component to ensure you’re selecting the correct type of screw.

This article has explained the differences between JIS and ISO screw standards, their compatibility, selection points, usage precautions, and how to choose between them. When selecting screws, it’s important to choose the appropriate standard, dimensions, material, and strength based on the intended purpose and environment. Additionally, understanding proper tightening torque, anti-loosening measures, and storage methods can help prevent problems related to screw usage.

Screws are small but essential components that support our daily lives. By selecting the right screws and using them correctly, DIY projects and machine maintenance can become safer and more efficient. We hope this article serves as a helpful guide for your screw selection. If you’re ever unsure which screw to choose, we recommend consulting a specialist or the manufacturer.

Conclusion

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