Table of Contents

Primer on Fastener Material

Fasteners are made in a wide range of plain and exotic materials, in addition, some fasteners are also available with a variety of coatings or platings to enhance corrosion resistance or appearance.
Fastener material can be extremely important due to the differences between material's brittleness, strength, corrosion resistance, galvanic corrosion, and cost.
When exchanging a faulty fastener with a new one, it is often important to match the material because of failure criteria (ie, a different material could be more brittle even though its harder)

Common Fastener Materials

Steel

Steel is the most common fastener material available. This material is available with a variety of coatings or platings. Steel fasteners are available in a variety of grades., namely grades 2, 5, 8, and alloy steel. Grades 2 and 5 are commonly plated with a blue or yellow zinc coating, or are galvanized to resist corrosion.

A Steel Fastener, Nut, and Washer

Steel Fastener Grades

These are some of the fastener grades available. Metric bolts and US bolts have different grading systems.

Grade 2

Grade 2 is standard hardware-store fastener material. This is the most commonly available fastener grade and bears no head marking, except for a possible manufacturers logo.

Grade 5 / Grade F

Grade 5 bolts are hardened during manufacturing to increase the fastener's strength and are the most common bolts found in the automotive industry. These bolts are identified with three 120-degree-spaced radial lines on the head. Grade F nuts are often used with grade 5 fasteners, as grades 5 and F are roughly equivalent.

Grade 8 / Grade G

Grade 8 bolts have been hardened more than grade 5 bolts. They are used for demanding applications like automotive suspension. This grade of bolt is identified by six 60-degree-space radial lines on the head.

Alloy Steel

Alloy steel bolts are made of a high-strength steel alloy and are further heat treated. Alloy steel bolts are typically not plated, resulting in a dull black finish. This grade of bolt is extremely strong but very brittle.

Stainless Steel

Stainless steel is an alloy of low carbon steel and chromium to increase its corrosion resistance. Stainless steel is very cheap for its corrosion resistance and because those same characteristics are inherent to the metal, it won't lose its corrosion resistance if scratched unlike some coatings. Stainless steel fasteners are generally stronger than steel fasteners but much weaker than hardened steel fasteners. Stainless steel fasteners are also extremely susceptible to seizing up during installation and cold welding, known as galling. Some different types of stainless steel are shown below:

Stainless Steel Fastener, Washer, and Nut

18-8 Stainless

This steel contains approximately 18% chromium and 8% nickel. This is the most common alloy for stainless hardware.

316 Stainless

A highly corrosion resistant grade of stainless steel. Ideal in salt water and chlorine environments, but more expensive than 18-8.

410 Stainless

A stainless alloy that is harder than 18-8 but not as corrosion resistant.

Silicon Bronze

Silicon bronze is an alloy of copper, tin, and silicon. This is a material typically used in marine environments, especially in wooden boat construction as it has a great corrosion resistance, while also being much stronger than brass. Silicon bronze is one of the most expensive fastener materials.

Silicon Bronze Bolt, Washer, and Nut

Brass

Brass is an alloy consisting mainly of copper and zinc. Brass is highly corrosion resistance and electrically conductive. It's use as a fastener material is limited as it has a relative softness compared to other materials. For this reason its often used for its appearance and not for its critical functionality as a fastener.

Brass Bolt, Washer, and Nut

Aluminum

Aluminum is light, soft, and corrosion resistant (scratches will not affect its corrosion resistance). Aluminum alloys are commonly used in fasteners, namely ones containing manganese, silicon, iron, magnesium, zinc. and copper. These elements affect the strength and melting point of the alloy which is beneficial for the fastener. Rivets are often made from 5000-series aluminum alloys which use magnesium as the primary alloying element.

Aluminum Bolt, Washer, and Nut

Complete Bolt Grade and Material Chart

This chart is a complete list of the common grades and materials in fasteners. It also contains information about strengths and failure limits. It also describes which grades and/or materials are available in which lengths and sizes.

References

"About Fastener Materials;“. BoltDepot.com. [Online]. Available: https://www.boltdepot.com/fastener-information/Materials-and-Grades/Materials.aspx [Accessed: 17-Dec-2020].

"Bolt Grade Markings and Strength Chart;“. BoltDepot.com. [Online]. Available: https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx [Accessed: 17-Dec-2020].

Image: albanycountyfasteners, "Aluminum Hex Bolts," https://www.albanycountyfasteners.com/mm5/graphics/00000001/Aluminum-Hex-Bolts-Product-1-(RESIZE)-min.jpg. [Online]. Available: https://www.albanycountyfasteners.com/mm5/graphics/00000001/Aluminum-Hex-Bolts-Product-1-(RESIZE)-min.jpg. [Accessed: 17-Dec-2020].

Contributors:

User	Last Update
Lesley Lang	1278 days ago

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