There are dozens of ways to join two products or materials, but fasteners supply the needed strength for a lasting connection, the ability to be quickly installed or removed, and the versatility to work with various materials in many applications. You’ll be reaching for a fastener when hanging the family portrait on the wall, fixing broken furniture, or building a backyard patio. These parts also provide structural integrity for heavy machinery, cars, buildings, bridges and more.
Choosing the right fastener is the hardest part, but this simple guide aims to break down the wide variety on offer, the crucial design and material differences, and how to size fasteners for your job.
Fastener Basics
Fasteners are hardware devices that mechanically join two or more objects together. Screws, bolts and nails are some of the most common types. While similar, they go about their purpose in different ways. Bolts and screws create a non-permanent joint and can be removed just as easily as they are installed, without causing harm to the joined materials or objects. They can also be reused. There are also permanent fasteners, such as rivets and screws, that create a lasting bond and cannot be removed without damaging both the fastener and the assembled items.
Common Types
Non-permanent fasteners can further be divided into two basic groups: threaded and non-threaded. Threaded fasteners have an integral thread, or elongated section, that does most of the binding. This thread not only secures the connected parts but also makes it easier to remove the fastener. It can then be reused as needed. Typical instances include the variety of bolts, screws and studs, and matching nuts (and washers).
Non-threaded permanent fasteners, like pins and retaining rings, often have lower holding strength. Non-threaded fasteners, however, are mostly of the permanent type once installed, and here nails, rivets and brads are the main types. Let’s take a closer look at some of the more common fasteners Australia-wide, and the ones you’ll likely use in your line of work.
Threaded Fasteners – Bolts, Screws and Studs
A helical or spiral thread running along part or the whole fastener body or shank offers several benefits. This includes high holding strength and durability, tightening (or torquing) adjustability, and easy installation and removal.
Bolts have an integrated head on one end and a thread on the other. Types commonly used in many industries are:
- Hex bolts – These are durable varieties with six-sided heads and partial threads, used in construction applications and machine assembly. Often paired with nuts to evenly distribute loads and tightened and loosened with a wrench.
- Coach/carriage bolts – Featuring a cup head, a smooth, non-threaded shoulder, and full or partial thread. These connect heavier metal or wood pieces.
- Structural bolts – These are heavy-duty hex-head bolts in larger sizes, made of high-grade galvanised steel, and used to connect steel elements.
- Roofing – These have a flat head, threaded body and a square nut to grip thinner metals and materials used in roofing applications.
Other bolt types are socket bolts tightened with an Allen wrench, larger track boots used in rail tracks, eye and U-bolts in overhead installations and many more.
Screws usually have rounded heads and longer threading, though are generally smaller and thinner, and have lower loading capacity than bolts. The most common types are wood screws with gentle threading to prevent splintering or wood damage; concrete screws when attaching wood or metal items into concrete and masonry, security screws with tamper-proof heads to prevent theft, self-drilling and thread-forming screws that drill their pilot holes without damaging the material, and chipboard screws used in processed wood products.
Screws and bolts with similar or identical designs, such as coach screws and bolts, usually differ in holding strength, and to a degree the thread length or design. In general, bolts are intended for medium to heavy loads, often in industrial settings, whereas screws are aimed at carpentry, woodworking, assembly and electronics. Their use is often regulated by set industry standards, determined among other factors by material grades and treatment methods.
Additionally populating the list of fasteners Australia-wide are fully or partially threaded studs, hex and locking nuts and a variety of washers (bevelled, flat, structural) used in conjunction with most bolts and some screws.
Non-Threaded and Permanent Fasteners
Nails are some of the oldest fasteners. They lack the holding strength of similarly-sized screws due to the absence of threading but can have higher shear strength, making them preferred in some applications, Typical variants include flathead nails with pronounced heads and thicker shanks, flooring nails often used to secure wood flooring, brads when attaching wood trim, plasterboard nails, larger framing nails in wood structural elements, and more.
Rivets are another popular non-threaded permanent fastener usually seen in electronics, automotive assembly and construction to secure metal or wooden pieces. They’re mostly chosen for their quick and simple installation (with rivet guns) and aesthetic appeal. Pop, drive and solid rivets are some of the more widespread types.
Lastly, anchors are permanent fasteners designed to hold heavy metal components in concrete, or epoxy resin. They can be installed while the concrete is curing, or after it has hardened. Mechanical anchors are inserted in a pre-drilled hole, while chemical anchors also require resin to ensure a secure connection. Both types are known for their exceptional holding strength and the ability to withstand high pullout and shear forces. Expansion shields, sleeve anchors, screw-in anchors and drop-in inserts are the most frequently used.
Head and Drive Types
Sourcing the right fasteners also means they need to work with your tools. This implies different head and drive designs. Hex heads, for instance, are often seen in bolts, but also coach and machine screws and are tightened and installed with wrenches. Other fastener head designs are ‘cheese’ heads that sit above the material, low profile button heads, raised or flat countersunk heads (when fasteners need to ‘disappear’ into the material), and socket-head fasteners tightened with an Allen wrench.
Moreover, there are different drive types, specifically for screws. Slotted and Phillips drives in common in wood screws, Torx and Pozidrives in specialty fasteners used in automotive and electronics applications, and hex socket drives where space is tight.
Materials
Most fasteners are metal affairs, but here too there is a lot of variety in terms of strength, heat, chemical and moisture resistance and overall durability. Stainless steel is the preferred material for high tensile and axial strength, good corrosion resistance, and lasting performance in numerous settings. Look for higher grades (304 and 316) when you need industrial-grade fasteners.
Carbon and mild steel types are good-quality and low-cost options, usually, zinc or hot-dip galvanised for better corrosion resistance. Decorative uses will see you using chromed, nickel-plated or brass bolts and screws. These also work well against high temperatures and in underwater applications with good resistance to rusting.
Where low weight and exceptional strength are the main prerequisites, such as aerospace or high-tech applications, go with aluminium or titanium. The materials are non-magnetic and also work well when exposed to water and heat.
Choosing the Right Sizes
Lastly, size matters. Diameters are that of the shank. In threaded fasteners, this is the outer part of the thread. Countersunk fasteners are measured across the whole length, while all other types, from just under the head to the tips. Keep in mind that measurements can be in metric or imperial units. And to ensure a tight and secure fit, also match bolts and screws with nuts and washers of corresponding sizes.