Types Measurement Material Finishes
Fastener Material
Not your ordinary material.
Carbon steel, alloy steel, aluminum, and stainless steel are just some of the materials that fasteners are manufactured in. The combination of material, heat treatment, hardening, and coating (a.k.a. finish) are essential to determining the strength and appropriate application for each fastener.
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If you need to replace a nut, washer, bolt or screw it is always recommended to perform an exact or matching swap. If a bolt is 304 stainless steel, we recommend replacing with 304 stainless steel. Furthermore, if a bolt is grade 5, we always recommend using grade 5 when replacing and not a lesser bolt grade.
Stainless Steel
Stainless steel is used primarily for long lasting applications, due to its corrosion-resistant nature and durability.
Scratching or burring the metal will not create surface rust as the corrosion resistance exists within the metal itself. Stainless is a soft metal due to the low carbon content, therefore most stainless steel bolts are cold-formed and not heat treated or thru-hardened. Cold forming and threading cause stainless bolts to become slightly magnetic, some fasteners will be more magnetic than others depending on size and how quick the cold forming process is. Stainless fasteners are typically a clean silver color, which also makes them common in finishing and decorative applications.
St. 304
304 stainless steel is the most commonly used grade for stainless fasteners. They are corrosion-resistant and durable. They are often used in marine applications in freshwater environments but will not work as effectively in a salt-water environment as 316 stainless. Stainless alloy resists oxidizing and rusting, however it can tarnish over time. This grade is equivalent to metric A2 stainless steel.
St. 316
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316 stainless steel is used and recommended for applications in severe, harsh or marine environments. Its corrosion resistance is greater than 304 stainless steel, which is why we recommend using 316 stainless steel fasteners for salt-water application. Common applications of 316 stainless fasteners include use on boats, docks, piers, and pools. This grade is equivalent to metric A4 stainless steel.
St. 410
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Harder than 304 stainless steel but with less corrosion resistance, 410 stainless is commonly used to make roofing screws, siding screws and self-drilling screws, because it is a harder material than the metal being fastened in these types of applications. 410 stainless steel can be hardened up to approximately 40 Rockwell C, making it durable in most environments.
Alloy Steel
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.
Grade 5 & 8.8
Grade 5 and Grade 8.8 alloy steel are medium carbon alloy steel that is heat treated to increase hardness. Grade 5 hex cap screws have three (3) evenly spaced hash marks on the head. Grade 8.8 hex cap screw have '8.8' marked on the head.
74,000 - 85,000 psi
Proof Load
81,000 - 92,000 psi
Minimum Yield Strength
105,000 - 120,000 psi
Minimum Tensile Strength
Grade 8 & 10.9
Grade 8 (inch) and Grade 10.9 (metric) alloy steel are medium carbon alloy steel that is heat treated to increase hardness. Grade 8 hex cap screws have six (6) evenly spaced hash marks on the head. Grade 10.9 hex cap screw have '10.9' marked on the head.
120,000 psi
Proof Load
130,000 psi
Minimum Yield Strength
150,000 psi
Minimum Tensile Strength
A325 & A490
ASTM A325 and ASTM A490 are heavy hex bolts intended for use in structural connections. Structural bolts features a wider bearing surface over which to distribute the load. They also feature shorter threaded to avoid interference with the joint.
120,000 psi
A325 Minimum Tensile Strength
150,000 psi
A490 Minimum Tensile Strength
A307 Grade 2 & 4.8
Carbon Steel
Carbon Steel is the most common and economical fastener material. Steel fasteners are available plain as well as with various surface treatments such as zinc plating and galvanization.
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Carbon steel fasteners are commonly available in A307 (inch) and Grade 4.8 (metric). Many other grades exist but are used far less often.
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A307 and Grade 4.8 are available in plain finish, plated with yellow or white (bright) zinc, or hot-dipped galvanised, to resist corrosion.
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Solid Brass
Brass is an alloy made of copper and zinc. The color of brass can vary from dark to light based on the zinc content; more zinc content produces lighter brass. Brass is prized for its corrosion resistance; however it is quite soft so it is not suitable for all applications. Brass conducts electricity and is also a good conductor of heat. It is often used in pipes, weather stripping, trim, radiators, musical instruments, and firearms.
Aluminum
Aluminum is a common material that is very soft and lightweight. Like stainless steel, aluminum's corrosion resistance is inherent to the material. Therefore, scratches and nicks will not effect the corrosion resistance.
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Aluminum alloy may be comprised of several materials including iron, manganese, silicon, copper, zinc and silicon. Aluminum rivets are among the most common aluminum fasteners.
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All Information provided in this page serves as a guide and not for reference purposes. Citi Bolt Group does not guarantee or warrant the accuracy or reliability of any information in our fastener guide. Citi Bolt Group accepts no responsibility for any loss or damage whatsoever resulting from reliance on the information provided.