Understanding Fasteners: A Beginner's Guide to Fasteners 101

Fasteners are essential elements in numerous applications, providing reliable and precise connections between materials. Serving as the foundation for both basic and intricate mechanical structures, fasteners are available in a variety of types such as screws, nuts, bolts, washers, and locknuts. They play a crucial role in industries ranging from construction to aerospace, quietly exerting a significant influence on our daily lives. Whether simple or intricate, these often-overlooked components are the unsung heroes that drive the functioning of our world, a role they have fulfilled for millennia.

Once you delve into the realm of fasteners, you will begin to notice them everywhere - on buses, trains, airplanes, phones, watches, and virtually every other object you interact with on a daily basis.

Short History

The screw was one of the last simple machines to be invented, first appearing in Mesopotamia during the Neo-Assyrian period (911-609 BC), and later in Ancient Egypt and Ancient Greece, as described by the Greek mathematician Archytas of Tarentum (428–350 BC). By the 1st century BC, wooden screws were commonly used in the Mediterranean world for pressing olive oil and grape juice.

Metal screws as fasteners were uncommon in Europe before the 15th century. The metal screw became a common fastener with the development of machine tools for mass production in the late 18th century. The Wyatt brothers from the UK pioneered one path with their screw machine in 1760, while Jesse Ramsden invented the first satisfactory screw-cutting lathe in 1777. Henry Maudslay further popularized screw-cutting lathes, leading to industrial machining advancements.

In 1821, Hardman Philips established the first screw factory in the United States for manufacturing metal screws. The turret lathe and automatic screw machines developed in the 19th century significantly reduced the cost of threaded fasteners, leading to increased screw usage.

The 19th century saw the use of simple screw head types like internal-wrenching straight slots and external-wrenching squares and hexagons. Precision screws for motion control emerged around the 19th century, playing a crucial role in the industrial revolution alongside flat surfaces. Standardization of thread forms further improved in the late 1940s with the definition of the ISO metric screw thread and the Unified Thread Standard.

(for more details: https://en.wikipedia.org/wiki/Fastener)

The most frequent varieties of fasteners consist of screws, which are threaded fasteners with external helical grooves that can be tightened or loosened by twisting the head. Screws can be inserted into pre-drilled holes in components, or they can create their own thread. A key distinction between a screw and a bolt is that the latter is intended to be tightened or loosened by applying torque to a nut. Additional types of fasteners encompass nuts, rivets, washers, nails, and anchors.

All these Heads... (at least the most common ones)

Flat screw heads sit entirely flush with a surface, leaving none of the heads exposed. These types of screws require you to countersink them. Their benefit that you won't have to worry about your screw sticking out from the surface and causing other things to catch on it.

Raised/Oval heads, sometimes known as oval-shaped heads, have an angle much like flat screws but have more of a dome-shaped head. You'll also need to countersink these screws to accommodate the angle. Unlike a flat screw, the head of a raised screw will come out of the surface slightly which has more of a decorative purpose.

Bugle heads are used mainly on screws made for plasterboard and drywall. This shape is much like a flat screw head, except that, instead of an angle underneath the surface of the head, you'll see a curved shape that can reduce damage to a surface. Bugle heads are self-drilling, so you won't need to drill any pilot holes before using them.

Domed heads are one of the most common types you'll find. These are ideal for projects that don't require you to hide the head of the screw. The dome shape creates a visually appealing design on the surface, while the flat inner part of the dome helps the screw stop where it needs to just at the surface.

Flange screws are sometimes referred to as frame screws. The head of these screws can vary from circular to hexed, and it juts out from a circular flange directly underneath the head. The flange helps the screw to remain in its position, taking the place of a washer for some projects.

Truss heads are typically wider than the heads on other screws and have a slightly rounded surface. You'll usually need truss heads when working with sheet metal and other projects that require large holes because the wide head prevents the truss screw from going through the hole.

Button screw heads come in a variety of sizes and lengths, and their common characteristic is a small, round, button-shaped head, hence the name. They can be flat or slightly rounded, but they always have heads that look like small buttons.

Pan head screws are machine screws with sides that are rounded and flat tops. Used in many applications that require a flat-bottomed screw, pan heads are the most common type of rounded screws. You can successfully substitute pan heads for other round styles.

Hex Heads are designed to allow for greater torque, hex heads typically require a wrench or socket to install the screw or bolt. Apply force against the screw head's outside to drive this head shape.

Socket cap Heads are usually shaped like a hexagon or round-shaped. Cap screws come in various lengths and materials, but each of them has heads that look like they're wearing a cap. These heads are unique to socket drive recesses and are installed flush against the surface.

All these Drives .... (at least the most common ones) These are the most common drives, it’s not an exclusive list:

The slot drive features a lone slot in the head of the fastener. This was the initial screw drive type to emerge, and for many years, it remained the most basic and cost-effective option. Although still utilized in certain scenarios requiring minimal torque, the slotted screw is not ideal for power tool installations.

The creation of the Phillips screw design aimed to address various issues associated with slotted screws, such as higher chances of cam out, the need for accurate alignment to prevent slippage and potential damage to the driver, fastener, and surrounding surfaces, as well as the challenge of using power tools for driving.

The Pozidriv screw drive, labeled as "Type IA" according to ANSI standards, is an enhanced iteration of the Phillips drive. It was specifically developed to enable increased torque application and better engagement compared to Phillips drives, thereby reducing the likelihood of loosening.

A Robertson screw drive, also known as a square screw drive, is designated as ANSI Type III Square Center. It features a square-shaped socket in the screw head and a square protrusion on the tool, both with a slight taper. Robertson screwdrivers are commonly used in woodworking and are convenient for one-handed operation due to the tapered socket that helps secure the screw, even when shaken.

The hex socket drive features a hexagonal recess that can be operated using a hex (Allen) wrench or hex bit. Its lever arch mechanisms enable higher tightening torque, while safeguarding the fastener's contact surfaces from external harm.

Torx/Star drive screws feature a 6-point star-shaped design that allows them to withstand higher torque and provide improved resistance to cam-out. They are commonly used in the automotive, computer, and consumer electronics sectors, and are becoming increasingly popular for construction applications.

One-way screws can only be rotated in a single direction. While they can be put in place with a regular flat blade screwdriver, they are not easily extracted with standard tools. These screws are frequently employed in commercial restroom fittings and on vehicle license plates to deter vandals from interfering with them.

All these different Threads ... When it comes to fasteners, the choice of threads varies depending on the application. In this discussion about various screws, our main focus will be on the different types of threads.

All these different Materials ...

Manufacturers commonly utilize steel for manufacturing high-quality fasteners. Approximately 90% of the bolts and screws produced annually are crafted from steel due to its durability, high tensile strength, and cost-effectiveness in fabrication.

Stainless steel is a widely used and dependable material for fasteners. With a chromium content of at least 10.5%, it offers corrosion resistance, making it well-suited for products exposed to high humidity or harsh weather conditions. Additionally, it boasts high strength and durability, making it an ideal choice for fasteners in marine settings, outdoor constructions, and food processing machinery.

Due to the presence of tin and copper alloy, bronze fasteners rarely rust, making them suitable for applications in aquatic environments such as underwater construction.

Brass, a copper and zinc alloy, shares comparable electrical conductivity and corrosion resistance with bronze. However, brass is softer and has lower tensile strength.

Aluminum is a lightweight, soft metal that is resistant to corrosion due to its inherent properties. As a result, the corrosion resistance of aluminum is not affected by scratches or nicks.

All these coatings ...

Coating is mainly done to prevent corrosion, although it can also serve as lubrication for threads and for aesthetic purposes in industries such as furniture. Fastener finishes and coatings are typically applied through electroplating, dipping, or spraying methods.

Self-color/Plain fasteners, as described here, do not have any extra coating. Typically, they undergo oil quenching, resulting in a surface oil residue that offers a basic level of protection.

Fasteners with zinc plating, especially those made of steel, undergo electroplating with zinc to enhance their resistance to corrosion. Zinc is the preferred material for electroplating fasteners, with zinc alloys like zinc-nickel and zinc-iron also being used. This process involves applying a thin zinc coating to the fasteners, providing them with a protective layer against environmental factors. The electroplating of fasteners is commonly referred to as barrel plating.

Chromate Passivation creates a protective layer of metal oxide on the zinc coating of bolts or screws, enhancing corrosion resistance and allowing for color coding. Chromates have a long history of use in passivation processes for their effective corrosion protection properties.

Hot Dip Spun Galvanizing HDS is considered one of the most efficient and cost-effective methods for corrosion protection. The zinc finish achieved through hot dip spinning is less shiny and smoother compared to electroplated zinc coatings. This process entails immersing the fastener in molten zinc, followed by centrifuge spinning to ensure an even zinc distribution and remove any excess coating. The average coating thickness is around 50 microns (µm), making it the thickest zinc coating for fasteners, thereby enhancing their resistance to corrosion.

How do I choose the right one??

When choosing the appropriate fastener, various factors should be taken into account. These include assessing the load capacity, the compatibility with the material, evaluating the environmental conditions and accessibility, considering the cost, ensuring compliance with industrial standards, and also contemplating the visual appeal. The realm of fasteners is significantly intricate, encompassing a wide array of head types, thread variations, drive mechanisms, materials, and coatings, each designed for specific purposes and applications.