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Bolt Grades, Strength & Materials

Fastener Material and Finish Information - From Alloy to Zinc

Fastener Grades

Alloy steel, aluminum, brass, silicon bronze, and stainless steel are just some of the materials that fasteners are manufactured in. The combination of material, treatment, hardening, and coating (aka plating) are essential to determining the strength and appropriate application for each fastener. Make comparisons on metals such as 304 vs 316 stainless steel to determine what grade you need.

If you need to replace a nut, washer, bolt or screw it is always recommended to perform and exact or matching swap. If a bolt grade is stainless steel, we recommend replacing with stainless steel. Furthermore, if a bolt grade is 316 stainless steel, prized for extra corrosion resistance, we always recommend using 316 when replacing and not a lesser grade such as 304 or 303.


How to Identify a Fastener Material:


  • Stainless Steel

    stainless steel socket cap screw316 stainless steel washersstainless steell nut

    Stainless steel is used primarily for long lasting applications, due to its corrosion-resistant nature and durability. Stainless Steel grades are rated by number. Scratching or burring the metal will not create surface rust as the corrosion resistance exists within the metal itself. Stainless steel 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 causes stainless steel 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 steel fasteners are typically a clean silver color, which also makes them common in finishing and decorative applications.Check out all of the Stainless Steel Fasteners we sell. Stainless Steel should never be used with aluminum, corrosion may occur. Several Stainless Steel grades are available:

    • 18-8 Stainless Steel:

      (18% Chrome, 8% Nickel, .08% Maximum Carbon) – 18-8 Stainless refers to 300 series stainless steel. 303 and 304 Stainless are the most commonly listed grades, the standard grade for stainless steel 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. Equivent to metric A2 Stainless Steel.

    • 305 Stainless Steel:

      (17%-19% Chrome, 8%-10% Nickel, .12% Maximum Carbon) - This stainless steel grade has been developed specifically to improve the cold heading qualities of 18-8. Corrosion resistance and physical qualities are equal to Type 304. 305 stainless steel is most commonly used to make deck screws, which are used to fasten wood or composite boards to the main beams of a deck.

    • 316 Stainless Steel:

      (16%-18% Chrome, 10%-14% Nickel, .08% Maximum Carbon, 2.00% Maximum Molybdenum) – This grade of stainless steel is used and recommended for applications in severe, harsh or marine environments. Its corrosion resistance is greater than 18-8 stainless, which is why we recommend using 316 stainless steel fasteners for salt water application. It is important to remember that even the salt in the air near a body of salt water can do damage to dry applications, so 316 is the material of choice. Common applications of 316 stainless steel fasteners include use on boats, docks, piers, and pools.

    • 410 Stainless Steel:

      (11.5%-13.5% Chrome, .15% Maximum Carbon) – Due to the fact that this stainless steel grade can be hardened up to approximately 40 Rockwell C, it is durable in most environments. Harder than 18-8 stainless but with less corrosion resistance, 410 stainless is commonly used to make roofing screws, siding screws and self tapping (or self drilling) screws, because it is a harder material than the metal being fastened in these types of applications.


    Is Stainless Steel Magnetic?

  • Silicon Bronze

    silicon bronze screw silicon bronze nutsilicon bronze washer

    Silicon bronze fasteners are made of copper, silicon, and various other alloys such as zinc, tin, iron and manganese. The color of silicon bronze may vary based on the amount of copper in the fastener. Silicon Bronze is superior in corrosion resistance to 316 stainless steel, it is more expensive than most fasteners. Silicon bronze is used in marine environments, corrosive environments, high heat environments, and it is suitable for use in standard applications for aesthetic purposes. Often used in plumbing and electrical applications, silicon bronze fasteners are also found on tattoo machines and in power plants. Silicon bronze is similar in color to copper and is sometimes used in finish applications for the color. Check out all of the Silicon Bronze Fasteners we carry.

  • Brass

    brass screwbrass nutbrass washers

    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. Check out all of the Brass Fasteners we carry.

  • Aluminum

    Aluminum Rivets

    Aluminum is a common material that is very soft and lightweight. 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. Aluminum should never be used with Stainless Steel, corrosion may occur.

  • Alloy Steel

    steel bolt steel allen wrench

    Alloy Steel is the most common material that fasteners are manufactured in. Alloy steel fasteners are often treated, coated or plated with zinc for additional corrosion resistance. Alloy steel is used for the hot dipped galvanized process, treated in a molten zinc bath which creates a tightly bonded alloy finish. Alloy steel is most often available in Grade A, Grade C, Grade 2, Grade 5 and Grade 8. Untreated alloy steel fasteners are black.

  • Zinc Plated Steel

    steel bolt

    Zinc Plated Alloy Steel is a common material that fasteners are manufactured in. Zinc plating creates corrosion resistance and gives the bolts a shiny finish. Zinc plated alloy steel is most often available in Grade A, Grade C, Grade 2, Grade 5 and Grade 8. Untreated alloy steel fasteners are black. Check out all of our Zinc Plated Steel Fasteners here.


    • Bolt Grades & Head Markings:

      Head markings on a bolt are a quick way to determine bolt grade. Some bolts will have additional markings that indicate the manufacturer; the most prized bolts have clean heads with limited markings.


      • Grade 2 / Grade A

        grade 2 steel bolt

        Grade A and Grade 2 are the most common grades of zinc plated alloy steel. Case hardened low or medium carbon steel. No head markings (manufacturers mark may be included).

      • Grade C

        grade c steel bolt

        Grade C is a thru-hardened medium carbon zinc plated alloy steel. No head markings (manufacturers mark may also be included). Finish is equivalent in strength to Grade 8 but without the yellow color.

      • Grade 5

        Grade 5 Steel Bolt

        Grade 5 alloy steel is a medium carbon zinc plated alloy steel that is heat treated to increase hardness. Grade 5 bolts have three (3) evenly spaced hash marks on the head markings (manufacturers mark may also be included).

      • Grade 8 / Grade G

        Grade 8 Steel Bolt

        Grade 8 zinc plated alloy steel bolts are thru-heated and thru-hardened with a CR+5 zinc plating. This treatment adds a superior strength and corrosion resistance, to the extent that they are often used for armored vehicles and vehicle suspensions. Grade 8 bolts have six (6) evenly spaced hash marks on the head markings (manufacturers mark may also be included).


Fastener Finishes:

  • Black Oxide black oxide stainless steel screwblack oxide stainless steel nutblack oxide stainless steel washers

    Black oxide fasteners are stainless steel fasteners that have been chemically treated to alter certain qualities of the material, most notably the color. The treatment adds a mild corrosion and abrasion resistance and reduces the now black oxide stainless steel fasteners reflective properties. To achieve maximum corrosion and abrasion resistance, the black oxide is sealed with oil and the excess is spun off, which complies with military specifications as a Class 4 finish. Black oxide fasteners are commonly used in the following industries: automotive, motorcycle, guns, knives, archery. Check out our selection of Black Oxide Fasteners by clicking the link.

    What is Black Oxide?


  • Hot Dip Galvanizing hot dipped galvanized bolt hot dipped galvanized square washer hot dipped galvanized washers

    Hot dip galvanizing is a process that adds a layer of corrosion resistance by dipping fabricated steel into a kettle containing molten zinc. The HDG process creates a tightly bonded alloy for superior corrosion resistance and harsh environment applications. HDG products must be used exclusively when applied, meaning that a plain zinc nut or stainless nut cannot be applied to an HDG bolt. HDG nuts are threaded slightly larger than other nuts to make room for the thickness of the galvanized coating. Check out our selection of Hot Dipped Galvanized Fasteners by clicking the link.

    All About Hot Dip Galvanized:


  • Zinc Plating zinc plated lag screw zinc plated wing nut zinc plated washers, zinc plated bolts

    Zinc plated steel is very common in the fastener industry. Zinc adds a layer of corrosion resistance to plain alloy steel. Clear zinc has a light, shiny color and blue zinc has a bright blue hue. Zinc plated steel is not suitable for extreme environment use, as it is not as resistant to corrosion as hot dipped galvanized. Check out our selection of Zinc Plated Fasteners such as zinc plated bolts, screws and wingnuts and Grade 8 Zinc Plated Fasteners by clicking the links.


  • Blue Climaseal® tapcon masonry screwblue masonry screw

    Blue coating applied to masonry anchors that provides extra corrosion resistance. Uniquely applied in multiple stages through dip-spin technology. This finish is used in our Tapcon Masonry Screws.