Duplex Steel Bolts vs Nuts – What’s the Difference

When choosing the right fasteners for your projects, knowing the differences between various materials is important. Duplex steel bolts and nuts are popular for industrial use due to their strength, corrosion resistance, and durability. But what exactly sets these two fasteners apart? This blog post delves into the key differences between Duplex steel bolts and nuts.

Difference Between Duplex Steel Bolts and Nuts

The primary difference between Duplex Steel Bolts and Nuts is their purpose. Duplex Steel Bolts are fasteners holding two or more components together, while Nuts are used to secure the bolt. Both work together to provide a strong connection. Additionally, Duplex stainless steel’s chemical composition provides better corrosion and pitting resistance than regular stainless steel, making it ideal for demanding applications, including marine construction and ocean water treatments. This also makes it a good choice for high-pressure pipelines subject to heavy wear and tear from high levels of organic compounds in water systems.


Depending on the specific application, duplex steel bolts and nuts are composed of various materials. Generally speaking, duplex bolts will be made from an alloy such as 316 stainless steel, while the corresponding nut is usually constructed from a carbon-based alloy such as A563 grade 10nut. These two compositions provide high strength and corrosion resistance to each component to handle demanding applications. The complex combination of metals ensures that these components can offer superior durability even when exposed to extreme temperatures and harsh environments.

Thread types

Duplex steel bolts and nuts may have different thread types. Bolts typically have external threads, while nuts have internal threads. This means that bolts can be screwed into nuts, providing a secure grip and easy installation and removal. Nuts can also be used to attach bolts to surfaces. The threads on bolts and nuts can be either coarse or fine, depending on the application’s specific requirements.

Size and shape

Duplex Steel bolts and nuts are generally shaped differently. Bolts have a uniform cylindrical head that projects from its diameter, while nuts have an internal thread. The size of the bolt or nut is determined by the nominal size of the bolt, which typically ranges from #0 to #20 (also in metric sizes). For a given nominal size, there are normally two different thicknesses of bolts and one standard width for all nuts. Due to differences in shape and strength requirements, using a nut larger than or smaller than its corresponding bolt isn’t recommended. Regarding material composition, Duplex Steel bolts and nuts perform better than other materials because they offer superior corrosion resistance when exposed to harsh environmental conditions.

Surface finish

The surface finish of duplex steel bolts and nuts can also vary. Bolts may have a plain or galvanized finish, making them resistant to corrosion and rust. Some bolts, such as Teflon, may also have a coating to provide even greater protection against wear and tear. Nuts may be finished similarly but coated in a lubricant to ensure they can be screwed onto bolts easily.


Duplex Steel Bolts and Nuts are commonly used for superior strength, corrosion resistance, and durability. They are primarily employed in oil & gas, chemical processing, marine engineering, power generation and construction. Duplex steel bolts offer unique advantages in comparison to standard carbon steel bolts – they’re stronger than other steels due to a higher tensile strength; they exhibit high corrosive resistant properties by forming a passive layer on the surface; and they offer greater fatigue strength which allows them to endure high amounts of pressure over long periods without breaking. This makes them ideal for applications involving extreme temperatures or environments exposed to saltwater.


In conclusion, duplex steel bolts and nuts have similar properties but differ in composition, thread types, size and shape, surface finish, and applications. When selecting these fasteners, it’s important to consider the application’s specific requirements to ensure the right fit and function. Whether you’re working on an offshore oil rig or a chemical processing plant, duplex steel fasteners’ durability and corrosion resistance make them an excellent choice for any industrial location.