Fasteners: Attributes to Consider - Part 1

Simply put, fasteners help secure or hold objects in place or together mechanically. You would think this concept is not complicated, but think again.

There are an infinite number of shapes, sizes, lengths, and varieties of fasteners. They can be commercial or specifically designed to fit an application. Every original equipment manufacturer (OEM) has a different and unique use for these valuable tools.

The wide range of fasteners includes screws, nuts, bolts, and washers in assorted sizes, types, materials, plating finishes, or patches and configurations. Their use, exposure, vibrations, stress, and pressure contribute to decision-making.

Fastener Categories: Permanent and Non-Permanent, Threaded and Non-Threaded

There are several ways to distinguish, classify, and categorize fasteners, including permanent and non-permanent, threaded, and non-threaded.

In the permanent classification are rivets and couplings that cannot be removed. Screws and bolts fall into the non-permanent threaded category, while rivets and blind fasteners are examples of non-threaded and permanent fasteners.

Non-permanent fasteners can easily be removed without damaging the secured materials. Permanent fasteners are designed to be a long-lasting form of secure connection.

Fastener Base Material Choices 

The base material of the fastener also plays a critical role. Depending on the application, factors such as environmental conditions, vibrations, stress, durability, and other factors contribute to such a decision.

Most fasteners consist of steel; however, the type of steel can vary. They can consist of carbon steel, stainless steel, alloy steel, or other types of steel. Choosing the suitable steel variety is based on that steel type’s properties, including formability, durability, tensile strength, and exposure responsiveness.

Fasteners have applications in all industries, and they are produced from a variety of materials. Many of these materials are differentiated in grades to indicate special alloys.

Carbon Steel Fasteners

Carbon steel fasteners are black in color due to their carbon content. The percent of carbon can vary by weight from low-carbon steel to high-carbon steel. These are used widely in automobile and building industries because of their strength, durability, and resistance to environmental conditions.

Grades 2, 5, and 8 are typically the standards for these carbon steel fasteners—grade 5, which is medium carbon steel and is widely used in automotive applications.

Carbon Steel Grade 2: This is the standard steel grade for hardware. The grade 2 bolts may feature a manufacturer’s mark.

Carbon Steel Grade 5: This is also known as grade F and is used in automotive applications. The bolts made from grade 5 feature radial lined heads.

Carbon Steel Grade 8: These bolts are harder than grade 5 and are used in demanding applications such as automotive suspensions and high-stress environments.

Alloy Steel Fasteners

Alloy steel bolts are strong but can be brittle. Alloy steel contains a high percentage of alloying elements other than iron and carbon. In contrast, carbon alloy has high carbon content and a low percentage of different parts.

Alloy steel is mixed with several alloying elements such as silicon, chromium, molybdenum, boron, vanadium, nickel, aluminum, and other elements. These alloying elements increase the steel’s strength, toughness, hardness, and wear resistance. Stainless steel is a type of alloy steel.

Stainless Steel Fasteners

Stainless steel has many benefits when used in fasteners. First, it has high corrosion resistance. Stainless steel does not rust or tarnish, giving you a better look and a longer lifespan.

Secondly, stainless steel increases material strength and will hold up in harsh corrosive environments. It will also hold up in place with extremely high or low temperatures.

Most stainless steel contains about 18% chromium. Chromium is what hardens and toughens steel. Nickel is used as a component in stainless steel, among other steel.

Nickel offsets the decrease in such toughness caused by chromium. Nickel also enhances corrosion resistance at elevated temperatures. However, the critical purpose of adding nickel is to ensure the steel is intact at and below room temperature.

Aluminum Fasteners

This material is soft, lightweight, and corrosion-resistant. Aluminum fasteners retain their corrosion resistance even if scratched or nicked during installation or regular use.

Various fasteners are made from unique aluminum formulations where elements such as iron, magnesium, silicon, and zinc (among others) are added during the process. Rivets are commonly made from aluminum alloys in the 5000-series, which uses magnesium as the primary alloying element.

Brass and Bronze Fasteners

These are the electrically conductive copper alloy. Since bronze is non-magnetic and highly resistant to corrosion, these are widely used in ship construction. They are not commonly in use because of their high cost, however.

Brass is used mainly for aesthetic purposes rather than strength. Brass is also a corrosion-resistant material. Custom brass fasteners plate well and are used in many fluid-exposed applications.

Nylon Fasteners

This type of plastic is typically modified during production to make it tough to withstand the conditions that a standard fastener is exposed to. The nylon used to manufacture these fasteners can be made from several types of plastic.

Nylon fasteners are commonly used in environments where metal fasteners would not be a good idea. Examples include designing electronics where the manufacturer might be interested in insulating the product as much as possible.

Plastic is a substance that is not a chemically reactive (inert) product makes it useful in environments where harsh chemicals will be used.

Titanium Fasteners

Because of suitable corrosion resistance properties and sustainability at high temperatures, these fasteners are usually found in aircraft, medical, petrochemical, pulp, paper, and race car industries. Grades 2 and 5 are the most commonly used grades of titanium screws.

Titanium Grade 2: This grade is commercially pure titanium and the most common grade for screws.

Titanium Grade 5: This is an excellent grade with a superior strength-to-weight ratio for a unique combination of corrosion and high strength.

Types of Fastener Coatings and Platings

Coatings and platings are added to fasteners to ensure corrosion resistance and other protective purposes. They may also be added for decorative purposes (chrome) or conductive purposes (copper). Many fasteners are left plain. There are distinct types of plating’s and coatings applied.

Chrome Plated Fasteners

Fasteners can be chrome plated and polished for a nice appearance and have corrosion resistance like zinc plating. Polished chrome costs more. If you need more corrosion resistance, you can chrome plate stainless steel, preventing corrosion should the chrome be penetrated.

Zinc Plated Fasteners

Steel fasteners can be electroplated with zinc for improved corrosion resistance, but they will rust if the coating is destroyed or exposed to a marine environment. The fasteners have a shiny silver (clear) or golden (yellow zinc) appearance.

Hot-Dipped Galvanizing Zinc Plated Fasteners

Galvanizing also involves adding a layer of zinc to the fastener. Hot dip galvanizing applies the thicket possible zinc coating onto the metal, providing the most superior corrosion resistance. Galvanized bolts are incompatible with non-galvanized nuts due to the thickness of the layer. Hot-dipped galvanized fasteners are most often used outdoors.

Cadmium Plated Fasteners

Cadmium is another plating material used to increase a fastener’s corrosion resistance. It has a surface appearance ranging from bright silver to a yellowish color. Cadmium plating exhibits low friction and is often applied with a chromate coating to augment its resistant properties.

Cadmium is unsuitable for applications that involve direct contact with food. Its functional temperature maximum is 450 degrees Fahrenheit, but it is thermally treated at around 375 degrees after plating to reduce the risk of hydrogen embrittlement. Hydrogen embrittlement occurs when metals become brittle due to the introduction and diffusion of hydrogen into the material.

Nickel Plated Fasteners

Nickel plating is the most traditional form of the plating process, although present-day methods often incorporate a supplementary chromium coating to decrease the chances of metal tarnishing.

Nickel can be used to improve both corrosion resistance and aesthetic appeal for less burnished surfaces. Like cadmium, nickel must be thermally treated after plating to prevent hydrogen deterioration.

It is a more expensive plating material than cadmium and zinc but has a high-temperature limit of 1100 degrees Fahrenheit.

Phosphate Coated Fasteners

A phosphate coating is used to reduce friction wear and increase corrosion resistance in metal fasteners and is often applied as a post-plating addition.

The most common types of phosphate coatings are zinc, manganese, or iron-based mixtures that are affixed to the fastener surface through spraying or an immersion bath.

The advantages of phosphate coating include a reduced risk of hydrogen embrittlement and the coating’s ability to serve as a foundation for finishing treatments, such as painting.

Fastener Patching

Fasteners may lose grip over time for joined parts and endure constant vibration. A patch applied to the screw assists in avoiding this issue.

The threaded area of the screw is treated with a nylon dot or a layer that wraps entirely around it. The patch increases the prevailing torque and provides excellent vibration resistance, allowing the screw to be locked in any position when assembled.

Nylon-patched screws will maintain their grip even under constant vibration and low-level heat conditions, making them especially popular with the automotive and aerospace industries.

Types of Fastener Heads

A distinguishing feature between the several types of screws and bolts is their heads, which are designed to fulfill a particular function. The variety of heads is as expansive as the different types of screws.

Several examples follow:

Flat Screw Heads: Flat screw heads are countersunk and fit flush with the secured surface. They have varying angles from the top of the head to the threads.

Raised Screw Heads: A raised head or oval head are like flat head screws but have a domed head.

Domed Screw Heads: Domed screw heads provide a larger surface for the screw to stop turning.

Truss Screw Heads: A truss screw head is a broad but low profile with a large surface area. The head is slightly rounded but broader.

Flange Screw Heads: Flange screw heads provide a wide surface area and have an attached washer built into the screw head.

Pan Screw Heads: A pan head is slightly rounded with short vertical sides. The head is like the head on a carriage bolt without the square shape underneath the head.

Binding Screw Heads: Binding screw heads are like a pan head but thicker with a deeper slot and have a 10% larger bearing surface.

Type of Fastener Drivers

The drive part of a bolt or screw transfers torque or force from the driver to the bolt or screw and forces it into the material. There are several types of drivers designed to fit unusual or unique applications.

Examples include:

Slotted Driver: The slotted driver is the traditional type designed for flat-head screwdrivers.

Phillips Driver: A Phillips head has a simple cross shape that offers more surface area for turning the bolt or screw, which reduces the necessary force to insert the bolt or screw.

Pozi Driver: A Pozi drive is like a Phillips drive but has extra grooves to form a star shape look.

Torque Driver: A torque drive has a greater surface area, which makes it easier to turn and reduces the amount of slippage. A higher force can be applied with a torque drive, making the connection more secure.

Hexagonal Interior Driver: The hexagonal interior head can have an Allen or hex screwdriver inserted to attach it. This head shape allows for greater surface area for the transfer of force.

Hexagonal Exterior Driver: This hex drive allows sockets and spanners and has a large contact surface for applying increased force.

Combination Driver: Some screw heads combine two different types of drivers to make them compatible with two types of drivers. A typical combination is flat and Phillips.

Square Recessed Driver: Square recessed drivers have a square-centered head that works to prevent cam outs and slippage. A square tapered driver drives them.

Conclusion

We hope this article answers your questions on fastener attributes, such as material, category, and types of fasteners that you need to consider in your manufacturing process. In part 2, we will discuss numerous types of Fasteners and their uses.

If you want to improve your application effectiveness with the benefits of fastener products, reach out to us on our contact page. Our supply chain management experts are always ready and willing to assist you and answer your questions.