Fasteners are manufactured in a wide range of materials from common steel to titanium, plastic and other exotic materials. Many materials are further separated into different grades to describe specific alloy mixtures, hardening processes, etc. In addition, some materials are available with a variety of coatings or platings to enhance the corrosion resistance or alter the appearance of the fastener.
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Fastener material can be important when choosing a fastener due to differences between materials in strength, brittleness, corrosion resistance, galvanic corrosion properties and, of course, cost.
When replacing fasteners, it is generally best to match what you are replacing. Replacing a bolt with a stronger one is not always safe. Harder bolts tend to be more brittle and may fail in specific applications. Also some equipment is designed so that the bolts will fail before more expensive or critical items are damaged. In some environments, such as salt water, galvanic corrosion must also be considered if changing fastener materials. For more information see our About Galvanic Corrosion page.
Stainless steel is an alloy of low carbon steel and chromium for enhanced corrosion characteristics. Stainless steel is highly corrosion resistant for the price. Because the anti-corrosive properties are inherent to the metal, it will not lose this resistance if scratched during installation or use.
It is a common misconception that stainless steel is stronger than regular steel. In fact, due to their low carbon content, many stainless steel alloys cannot be hardened through heat treatment. Therefore, when compared to regular steel, the stainless alloys used in bolts are slightly stronger than an un-hardened (grade 2) steel but significantly weaker than hardened steel fasteners. Unless great care is taken, stainless fasteners are susceptible to seizing up during installation , a phenomenon known as galling.
Most stainless steel fasteners are much less magnetic than regular steel fasteners though some grades will be slightly magnetic.
Steel is the most common fastener material. Steel fasteners are available plain as well as with various surface treatments such as zinc plating, galvanization, and chrome plating.
Steel fasteners are commonly available in 4 grades: Grade 2, Grade 5, Grade 8, and Alloy Steel. Many other grades exist but are used far less often. Grade 2, 5, and 8 are usually plated with a slightly blue-ish or yellow zinc coating, or are galvanized, to resist corrosion.
Bolts are typically marked on the head to show what grade bolt they are. For a list of the most common grade markings see our Material Grade Identification and Properties Chart . Note that, in addition to the grade marking, many bolts also have a manufacturer's mark.
Grade 2 is a standard hardware grade steel. This is the most common grade of steel fastener and is the least expensive. Except a possible manufacturer's mark, Grade 2 bolts have no head marking.
Grade 5 bolts are hardened to increase strength and are the most common bolts found in automotive applications. Grade 5 bolts have 3 evenly spaced radial lines on the head.
Grade F is roughly equivalent to Grade 5. Grade F nuts are used with Grade 5 bolts.
Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stronger and are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head.
Grade G is roughly equivalent to Grade 8. Grade G nuts are used with Grade 8 bolts.
Alloy steel bolts are made from a high strength steel alloy and are further heat treated. Alloy steel bolts are typically not plated, resulting in a dull black finish. Alloy steel bolts are extremely strong but very brittle.
Silicon bronze, often referred to simply as bronze, is an alloy made mostly of copper and tin with a small amount of silicon. Bronze is used primarily in marine environments. It is preferred over stainless in wooden boat construction and re-fastening due to its superior corrosion resistance, and over brass due to its higher strength. Bronze is similar to copper in color and is also sometimes seen in fine woodworking where it is used for its appearance. The main drawback of bronze is its high cost.
Brass is an alloy of primarily copper and zinc. Brass is highly corrosion resistant and electrically conductive. However, its use as a fastener is somewhat limited due to its relative softness. It is used primarily for its appearance.
Aluminum is a light, soft, corrosion resistant metal. Like stainless steel, aluminum's corrosion resistance is inherent to the material. Therefore, scratches and nicks will not effect the corrosion resistance.
Fasteners are made from a variety of aluminum alloys, with elements such as manganese, silicon, iron, magnesium, zinc, copper, and silicon being added to increase strength and melting point.
Rivets are often made from aluminum alloys in the -series, which uses magnesium as the primary alloying element.
Fasteners are often an unnoticed, yet integral, part of any application that most people don’t give much consideration to until they need to use one. The material the fastener is made from is equally as important as their size specifications. Fasteners can be manufactured from a wide variety of materials and further enhanced by a range of coatings, platings, and finishing treatments. No matter what type of fastener you need – screw, peg, rivet, bolt, clamp, etc. – selecting the proper material for the intended application is critical to both performance and reliability.
In order to select the proper material for a fastener numerous factors need to be taken into consideration. There are four main criteria that need to be evaluated in order to select the proper fastener material. Those are:
The load or stress
When selecting a material to fabricate your fasteners from you must take into consideration the proof load, the yield strength and the tensile strength of the particular material.
Strength
The strength properties will be very different depending on which type of material is used to create the fastener as well as the final shaft length of the fastener, plus a few other considerations.
Typical metal strengths at room temperature:
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Typical polymer strengths at room temperature:
Typical ceramic strengths at room temperature:
Resistance properties
Corrosion wears metal down due to the material’s interaction with chemicals in the surrounding environment. The most common type of corrosion is oxidation, which is caused when the metal reacts to oxygen and rusts. Typically to combat corrosion, the fasteners will need a protective coating applied such as chrome or zinc. Otherwise, if applicable, the fastener could be manufactured from a material that does not corrode such as non-ferrous metals or plastic alloys.
Temperatures
You need to take into consideration the average temperatures that the fastener will be required to operate in to be sure that the material can handle it. Obviously plastics and non-ferrous alloys have no place in environments with extremely hot temperatures. Others can become brittle in extreme cold and lose their ductility.
What are the most common materials used to manufacture fasteners?
Here is a quick list:
What material would be best to select?
Fastener materials are typically selected based on their mechanical properties, potential for post-fabrication treatments, cost-efficiency, and a few other considerations. However, which material would be best for your application truly depends on what you need the fastener to join and where. In critical applications that will be exposed to extreme temperatures or corrosive environments it is best to select a material that is strong, can withstand the temperatures, and has good corrosion resistance.
Aluminum
Aluminum is a very popular and affordable material choice that provides manufacturers with a lot of versatility. Alone it is a great choice for lightweight, lower strength, applications that need the material to have good resistance to corrosion. If combined with other metal alloys, aluminum can have the strength of steel but with a fraction of the weight.
Brass and Bronze
Brass, an alloy of copper and zinc, is the most common copper based alloy used to manufacture fasteners. It provides decent resistance to corrosion, is relatively inexpensive, and has good electrical conductivity properties. Bronze, an alloy of tin and copper, boasts very high corrosion resistance. Both of these offer an attractive reddish-yellow color.
Steel
Steel is a popular fastener metal and comes in a wide variety of forms and strengths such as alloy steel, carbon steel, stainless steel, and many more. The corrosion resistance properties and mechanical strength of steel makes the material incredibly desirable for fasteners. The mechanical strengths range from approximately 50ksi (kilo-pound per square inch) to up to 300ksi.
Titanium
Titanium is one of the best choices for fastener manufacture, especially for high impact applications. It provides low weight, a high level of strength, as well as incredible resistance to both corrosion and wear.
Polymers
Engineered Polymers offer unique properties for specialty applications. Their temperature limits typically range from 100° C to just under 600° C. They also provide good corrosion resistance and offer decent tensile strength.
Ceramics
Few materials can withstand heat, pressure, and corrosion better than ceramics. However, they are not typically very strong; over-torque them a tiny bit and they will shatter. This makes them tricky to initially install which turns most people away from them.
Here is a quick reference table of the most commonly used fastener materials and their most notable properties:
Even the smallest component can ruin the effectiveness of a product or cause significant challenges, which in turn may determine a manufacturer’s success or failure. By partnering with experts like us in engineering and supply, manufacturers not only solve potential issues before they arise, but also boost safety, quality, speed to market, and profitability.
How can UC Components, Inc. help you?
While the right materials, coating, plating, or finishing treatment for your fastener application is best defined by your process engineer, we are always here to assist you. UC Components, Inc. has been the world leader in high vacuum hardware since .
UC Components, Inc.’s RediVac® fasteners, washers, nuts, and O-rings are designed for use in a wide range of high vacuum applications and clean-critical environments. We offer a variety of specialized venting designs, complete custom product development, numerous finishes, and Class 100/ISO Class 5 Cleanroom cleaning and packaging.
If you want to learn more, please visit our website 12l14 Lead Free Cutting Steel.