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.
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.
18-8 refers to any stainless steel containing approximately 18% chromium and 8% nickel. This is the most common stainless designation for hardware. For information on 18-8 stainless steel material properties see our Material Grade Identification and Properties Chart .
A highly corrosion resistant grade of stainless steel. Ideal in salt water and chlorine environments. More expensive than 18-8.
A stainless alloy that is harder than 18-8 stainless steel, but not as resistant to corrosion.
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 5000-series, which uses magnesium as the primary alloying element.
Many steel fasteners are electroplated with zinc for better corrosion resistance. Fasteners that have been zinc plated have a shiny, silvery or golden appearance, referred to as clear or yellow zinc respectively. They are fairly corrosion resistant but will rust if the coating is destroyed or if exposed to a marine environment.
Galvanizing is another coating involving the application of
a layer of zinc. Hot dip galvanizing puts the thickest
possible coating on the metal, resulting in superior corrosion
resistance. Due to the thickness of the coating hot dipped
galvanized bolts are not compatible with other nuts. Galvanized
nuts are tapped slightly larger than other nuts to accommodate
this coating.
Hot dipped galvanized fasteners are frequently used outdoors, especially in coastal
environments.
Fasteners are chrome plated and polished for appearance. Chrome plating provides similar corrosion resistance to zinc plating. The main drawback of polished chrome is its high cost. If more corrosion resistance is required, stainless steel may be chrome plated, preventing any corrosion should the chrome be penetrated.
SHOP BLACK OXIDE FASTENERS
Black Oxide, sometimes called blackening, is the act of converting the top layer of a ferrous material with a chemical treatment. Treating fasteners with a black oxide coating not only adds a nice clean black look but can also add a mild layer of corrosion and abrasion resistance. To achieve the maximum in corrosion resistance, black oxide can either be waxed or oiled to add an extra layer of protection. The wax coating may dull the color of the treatment but provides the best resistance. The black oxide treatment is also referred to as gun bluing.
When fasteners are dipped into the black oxide bath materials (warm and hot processes) the harsh chemical components convert the top layer into magnetite. Black Oxide Stainless Steel Nuts Bolts and Washers are the most common form of black oxide fastener available. Prized both for the corrosion resistance of stainless steel with the added benefits of the black oxide treatment.
Blackening can be achieved in a number of different ways. There are three main ways to do this. If you are interested in the specifics of each type check out this article from Wikipedia.
The process of treating the fasteners in different chemicals in order to convert the surface material into magnetite. The process is completed by dipping the fasteners into different tanks and occasionally placed in water. Once the process of dipping is completed the top layer of the fastener is porous and a layer of oil is applied. The oil seeps into the material adding that extra corrosion resistance to rust. This process creates a black oxide bath that complies with MIL-DTL-13924, AMS 2485, ASTM D769 and ISO 11408 standards.
The cold process applies a compound (copper selenium) onto the fasteners at room temperature. This process is more convenient for working in house as it does not require many chemicals at heated temperatures to apply. Once applied it is considered weaker than the other forms of oxidization until a layer of oil or wax is applied to the surface.
Like the hot bath treatment method but does not produce the same toxic fumes of the hot bath and the surface is converted to magnetite at a much lower temperature. This method can also meet the same military standards that the hot bath version produces.
Black Oxide adds a mild layer of corrosion and abrasion resistance to fasteners. Like any material, black oxide treated fasteners can rust in the right environments. It will depend on if the fastener is damaged or marred, the type of metal with the black oxide treatment and environmental conditions.
Black oxide is not nearly as corrosion resistant as some of the other options available to improve corrosion resistance.
The black oxide finish can be easily rubbed off. To prevent this, put some painters tape over the tip of your bit to create a tighter fit and prevent scratching in the event of a slip out of the drive.
The Black residue from the fasteners may come off of them so for certain applications it is recommended that they are wiped down before use. This extra step can be labor-some if many fasteners are needed.
Black oxide fasteners are largely used in the automotive industry due to their sleek black look. This look can deteriorate very quickly though in hot environments. Often, after a black oxide coat is applied to a fastener, they are placed in an oil bath for an extra layer of protection. The oil residue that stays on the fasteners will begin to turn brown when in high heat environments. So many users find they bolts look like they rust prematurely. It is not recommended to place black oxide bolts on or near engines.
SHOP BLACK OXIDE FASTENERS
Our company offers custom black oxide orders VIA phone orders. Can’t Find what you need in black oxide? Give us a call at 866-573-445 for pricing and availability!
Custom Fasteners and Hardware
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