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Fastener Materials, What are Bolts and Screws Made From?

Fasteners Inc

Get to Know the Various Fastener MaterialsAt Fasteners, Inc. in Denver, we know that the world couldn’t exist without fasteners. So, let’s get to know the various fastener materials. It’s really amazing how fasteners can do so many different things depending on what they are made out of and their design.

Most people have no idea that fasteners can be made from so many materials, including steel all the way to titanium and plastic. But that’s just the start. Then those materials can be divided into different grades to specify alloy mixtures, hardening processes, and other differences like coatings and platings that enhance corrosion resistance or alter the fastener’s appearance.

Why is the material important to a fastener?

What material the fastener is made out of will affect strength, corrosion resistance, brittleness, galvanized corrosion properties and cost.

Keep in mind, if you need any type of fastener, you should try to match the material that you are replacing. You need to consider the environments, like salt water and galvanic corrosion if you are changing fastener materials. Often trying to replace a bolt with a stronger bolt may jeopardize safety. A harder bolt may be more brittle and could fail in specific applications. Did you know that some equipment is designed so that the bolts will fail to protect the more expensive or critical parts of the equipment?

Now let’s examine what the different fastener materials offer for your project.

DIFFERENT FASTENER MATERIALS

Steel

The most common fastener material, steel fasteners can be plain or with various surface treatments such as zinc plating, galvanization, and chrome plating.

Stainless Steel

Stainless steel is an alloy of low carbon steel and chromium that offers enhanced corrosion protection. Its anti-corrosive properties will not lose its resistance if is scratched during installation or use.

Some people think stainless steel is stronger than regular steel. But it isn’t. In fact, because of the low carbon content, many stainless steel alloys cannot be hardened by heat treatment. So, if you compare stainless steel to regular steel, the stainless alloys often used in bolts will be slightly stronger than an unhardened (grade 2) steel, but they will be significantly weaker than hardened steel fasteners. One of the problems is, unless you are very careful, stainless fasteners can be susceptible to seizing up during the installation process. This is called galling.

Most stainless steel fasteners are much less magnetic than regular steel fasteners while some grades will be slightly magnetic.

Stainless 18-8

If the stainless steel contains approximately 18% chromium and 8% nickel, it is called stainless 18-8. It is the most common stainless designation for hardware.

Stainless 316

This is a highly corrosion resistant grade of stainless steel. It works well in salt water and chlorine environments. It is more expensive than 18-8 stainless.

Stainless 410

This is a stainless alloy that is harder than 18-8 stainless steel, but it’s less resistant to corrosion.

Grades

Steel fasteners are available in grade 2, grade 5, grade 8, and alloy steel and are usually plated with a slightly bluish or yellow zinc coating, or are galvanized to resist corrosion. There are other grades but they are not used very often. The grade is marked on the head of the bolt.

Grade 2

This is a standard hardware grade steel. It is the cheapest and the most common grade of steel fastener. Unless there is a manufacturer’s mark, Grade 2 bolts will have no head markings.

Grade 5 / Grade F

These are hardened to increase the strength and are most commonly found in automotive applications. These bolts have three evenly spaced radial lines on the head. Grade F is roughly equivalent to Grade 5 and Grade F nuts are used with Grade 5 bolts.

Grade 8 / Grade G

Grade 8 bolts are more hardened than Grade 5 bolts. This type of fastener is stronger and are used when a more demanding application is needed like in automotive suspensions. Grade 8 bolts have six evenly spaced radial lines on the bolt head. Grade G is pretty much equivalent to Grade 8. Grade G nuts are used with Grade 8 bolts.

Aluminum

This metal is light and soft, but scratches and nicks will not affect its corrosion resistance.

Fasteners can be made from different aluminum alloys, with elements like manganese, silicon, zinc, copper, iron, magnesium, and silicon being added to increase the strength and melting point. Rivets are commonly made from aluminum alloys in the 5000-series, which uses magnesium as the primary alloying element.

Alloy Steel

These bolts are made from a high strength steel alloy and are heat treated. They are not usually plated, so they have a dull black finish. Alloy steel bolts are very strong but somewhat brittle.

Brass

This is an alloy of mostly copper and zinc. Brass is highly resistant to corrosion and electrically conductive. However, it’s relatively soft and so, its use is limited. In fact, it is often used mainly for its appearance.

Silicon Bronze

Silicon bronze or bronze is an alloy made out of copper and tin and a small amount of silicon. This is often used in marine environments, used in wooden boat construction, and re-fastening because it is superior in corrosion resistance and strength. Bronze looks copper in color and is sometimes used for its appearance in fine woodworking. Bronze comes with a higher cost.

MORE OPTIONS, COATINGS

Chrome

Fasteners can be chrome plated and polished for a nice appearance and have corrosion resistance like zinc plating. Polished chrome costs more. If you need more corrosion resistance, you can chrome plate stainless steel, preventing any corrosion should the chrome be penetrated.

Hot Dip Galvanizing

This also involves an application of a zinc layer, which is the thickest possible coating on a metal. This makes it have superior corrosion resistance. You will need to use galvanized nuts because the thickness of the coating is not compatible with other nuts. Galvanized nuts are tapped slightly larger than other nuts to accommodate this thicker coating. These fasteners are used outdoors, especially in coastal environments.

Zinc Plating

Steel fasteners can be electroplated with zinc for improved corrosion resistance but they will rust if the coating is destroyed or exposed to a marine environment. The fasteners have a shiny silver (clear) or golden (yellow zinc) appearance.

As you get to know the various fastener materials, keep us in mind. We are Fasteners, Inc in Denver. We are an industrial distributor for the Huck Fastening System, including Magna-Grip, Magna-Bulb, Magna-Lok, C6L, C50L, BOM, Huck Automatic Rivets and Huck Industrial Tooling. Our extensive inventory is available for prompt delivery or shipment of materials, ranging from aluminum to stainless to heat-treated steel and almost everything in between.

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