Best & worst material for fasteners.

When it comes to fasteners many of us instantly believe the main consideration should be fastener type. Lets face it, the choice is endless from high strength Huck rivet Magna-Lok and Magna-Grip Huck bolts, through to Nutserts, Rivnuts, Plus Nuts and so much more. The truth is a lot more complicated, another important consideration should be the material of the fastener. Fasteners come in a wide range of different materials from everyday steel to shiny stainless-steel right through to brass, aluminium, nylon and so much more. At first glance it may seem simple enough – but there are a lot of other factors at play with each material having their own positive and negative attributes, along with different grade steels and coatings. 

Today’s article will touch base with the different type of materials used to make fasteners, their grades and the meaning behind the grades. When selecting fasteners ensure the material is compatible with the parent material to minimise galvanic corrosion. This process occurs when dissimilar metals along with atmospheric moisture combine with each other. As a general rule avoid using aluminium and stainless steel together; otherwise we recommend keeping the metal materials like for like for maximum life. Stainless with stainless, aluminium with aluminium.

Steel Fasteners. Steel grades: 2, 5, 8 and Alloy Steel. 

Most manufacturers use steel as their fastener material of choice, and it’s not hard to see why. Steel, regardless of grade, is a great all-rounder, with a high durability and strength and a fairly low cost of production. Steel comes in various surface treatments such as zinc plating, galvanization, and chrome plating.

The different grades of steel are dictated largely by how strong the steel is made. By heat treating the carbon within the steel, they can become stronger – but also more expensive. 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.

Steel Grade 2.

A standard grade low carbon steel  material in most fasteners. As it isn’t heat-treated like other grades, it is one of the cheapest materials you will find. Grade 2 standard bolts have no head marking. Huck bolt collars are grade 2 steel which allows for the swaging of the collar onto the pin. 

Steel Grade 5. (Grade F).

Meduim grade steel that is hardened via heat-treating to increase its strength. The increase in durability and corrosion resistance means they are often used 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. Huck bolt pins are grade 5 steel. 

Steel Grade 8. (Grade G).

Similarly to Grade 5, Grade 8 steel is heat-treated, but even more so than their Grade 5 counterparts. This makes Grade 8 steel one of the strongest material types for fasteners, and also one of the most expensive. 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. 

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.

Stainless Steel. Grade 304 and 316.  

Grade 304 stainless steel is generally regarded as the most common austenitic stainless steel. It contains a high nickel content, typically between 8 and 10 percent by weight, and a high amount of chromium, approximately 18 to 20 percent by weight. Other major alloying elements include manganese, silicon, and carbon. The remainder of the chemical composition is primarily iron. The high amounts of chromium and nickel give 304 stainless steel excellent corrosion resistance.

Like 304 stainless steel, Grade 316 stainless steel has high amounts of chromium and nickel. 316 also contains silicon, manganese, and carbon, with much of the composition being iron. A major difference between 304 stainless steel and 316 stainless steel is the chemical composition, with 316 stainless steel containing a significant amount of molybdenum, typically 2 to 3 percent by weight, compared to only trace amounts found in 304 stainless steel. The higher molybdenum content results in grade 316 stainless steel possessing increased corrosion resistance. 

Stainless-Steel 304 V's Stainless-Steel 316. When & Where to Use. 

If your application involves corrosive substances such as chloride, marine, or medical environments then paying a premium for grade 316 stainless steel is worth it. In such work applications, the 316 stainless steels will last longer than 304 stainless steels—this means many extra years of useful life. For other applications where salt or water exposure isn’t a concern, the stainless steel 304 alloy can work just as well. Just be sure you’ve accounted for all processes and environmental factors when choosing the material. For instance, if the application is located on or near the coast, salty sea air can corrode metals. Overall, 316 can be worth the expense if you need to have superior corrosion resistance. For many other applications, grade 304 stainless steel will serve perfectly fine.

Brass.

Brass is an alloy made of copper and tin. Making it a much softer than most other materials and primarily used for its gold-like look in home or marine decor where corrosion resistance and low friction are required, such as locks, screws and hinges. Plus commercial applications covering bearings, zippers, gears, hose couplings, valves and electrical plugs and sockets. It is also used extensively in the manufacture of musical instruments like trumpets, trumbones, bells etc. 

Aluminium.

Aluminium is a silvery-white, lightweight metal that is soft and malleable. Aluminium is used in a wide range of everyday products including cans, foils, fasteners, and window frames right through to the specialised manufacturing of aeroplanes, marine vessels and even aerospace applications. This is because it is a lightweight metal with a weight-to-strength ratio is actually quite high (99 to stainless steel’s 63) making it an ideal metal for numerous applications in aviation and marine where weight is an an important consideration.   

It's also important to note that aluminium is a great option for those looking to create a more sustainable project, as around 75% of aluminium that has been manufactured is still in use today. Which, when compared to steel’s 40%, you can see why it is a more desirable option for products that hold sustainability as a priority. Aluminium also has a number of different grades assocated which we will cover in another blog acticle.  

Coatings. 

Zinc Plating.

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.

Hot Dip Galvanizing.

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.

Chrome.

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.

Nylon.

Nylon is becomng a popular material for fasteners and other small components. Nylon fasteners are used in numerous situations including electrical and electronic units because nylon offers good electrical resistance. Being inert to most natural environmental conditions makes Nylon Fasteners useful in applications for medical and food sectors.

Fastener Material Summary.

Fasteners are manufactured in a wide range of materials from common steel to titanium, nylon, and other 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 all your industrial requirements, Aerobolt we have a comprehensive range of fasteners and can assist in your application, simply call us on 02 9755 3747 or contact us for all your requirements.

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