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:
  1. The load or stress
  2. Strength
  3. Resistance properties
  4. Temperatures
 
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.
  • The proof load, or stress, is measured in pounds per square inch and refers to the minimum acceptable load that the fastener will withstand. When it comes to fasteners, pure steel and low carbon steel have the lowest acceptable proof load.
  • The yield strength refers to the load at which the fastener will become permanently deformed.
  • The tensile (or ultimate) strength refers to the load that will break the fastener.
 
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:
Material Ultimate/Tensile (ksi) Yield Strength (ksi)
Inconel 718 210 175
Monel K500 160 110
Moly 158 130
Titanium Grade 5 148 138
Inconel 625 144 84
Tungsten (99.5%) 142 109
Super Duplex 2507 125 82
Duplex 2205 110 80
Tungsten Alloy 94-100 75
Molybdeum 94 90
Inconel 600 93 37
Zirconium 705 89 73
Aluminum 7075-T6 83 73
Monel 400 83 32
Titanium Grade 2 70 50
Nickel 200 60-85 15-45
Zirconium 702 68 47
 
Typical polymer strengths at room temperature:
Material Ultimate/Tensile (psi) Yield Strength (psi)
PEEK (extreme) 47900 51000
PEEK (glass fiber) 22800 26000
PEEK (unfilled) 16000 13600
Vespel 12500 -
Torlon PAI 22000 -
PVDF 5000-8000 6500-8000
PTFE 3900 1450
PFA 3600 2000
 
Typical ceramic strengths at room temperature:
Material Ultimate/Tensile (ksi) Yield Strength (ksi)
Zirconia 75 -
Alumina 30 -
 
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:
  • Metals, such as: Aluminum, Brass, Steel, Titanium, Magnesium, Molybdenum, Monel, Inconel, and many more.
  • Polymers, such as: Nylon, PEEK, PFA, PTFE, PVDF, Torlon, Vespel
  • Ceramics, such as: Alumina, Zirconia, and more.
 
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 noteable properties:
Aluminum Brass or Bronze Titanium Nylon
-Light
-Soft
-Corrosion resistant
-Relatively soft
-Corrosion resistant
-Electrically conductive
-Aesthetically pleasing
-Superior strength
-Extremely corrosion resistant
-Ideal for high-temp. environments
-One of the most commonly used plastics
-Exceptional strength
-Excellent wear resistance
 
Steel – Alloys Steel – Carbon Steel – Stainless Ceramics
-High strength
-Low corrosion resistance
-Often brittle or rigid
-Often requires additional coating
-Grades 2, 5, and 8 are standard for bolts and screws -Superior strength
-High corrosion resistance
 
-Good strength
-Extremely corrosion resistant
-Survive extremely high temperatures
-Non conductive
-Non magnetic
-Lightweight
-Reuseable
 
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 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 1974.
 
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.
 
Contact UC Components, Inc. to learn more or to request a quote today.
www.uccomponents.com