Fasteners: which material do I need?
3 minutes | 24 Aug 2018
What should you look for in a fastener? Here are just a few things to consider:
The project’s secured and you’ve mapped out a rough plan of action – but what about materials? Fasteners are likely to feature high on your list of priorities, but which kind is best? Manufactured in a wide variety of materials – from titanium to plastic and steel – fasteners can also be whittled down even further: by different grades. Describing a particular alloy mixture or hardening process, for instance, these grades help you make an informed decision when it comes to choosing the correct alloy fastener.
Available with a range of coatings or plating, used to enhance the component’s resistance to corrosion, different fasteners offer a different aesthetic, too.
- Corrosion Resistance
- Galvanic Corrosion Properties
In the instance where you’re replacing a fastener, it’s a good idea to match the component you’re replacing. Some equipment is designed so that its bolts will fail prior to more expensive or critical items being damaged, which is why it’s important not to simply replace a bolt with a stronger one. This is due to the fact that it could be more brittle and will have therefore have more chance of failing.
You must also consider the environment of your project. Salt water can lead to galvanic corrosion, for example, which will mean your fastener didn’t quite turn out to be quite as cost-effective as you first thought and hoped.
Let’s take a look at some of the key materials used in fasteners:
An alloy of low carbon steel and chromium, stainless steel offers enhanced corrosion properties, as well as a good price. Its anti-corrosive properties are integral to the material, and the component won’t lose this resistance if, for example, it is scratched during the installation process.
Be aware, though, that stainless steel isn’t stronger than standard steel; this is a common misconception. Instead, due to its low carbon content, stainless steel alloys often can’t be hardened during heat treatment. When comparing stainless steel to standard steel, you’ll find that the stainless alloys used in bolts are that bit stronger than grade 2 – an un-hardened grade. That said, they are quite a lot weaker than hardened, steel fasteners, and unless care is taken during installation and thereafter, fasteners made from stainless steel can seize up.
The most common stainless designation for hardware is 18-8 stainless, which refers to stainless steel containing around 18% chromium and 8% nickel. Meanwhile, stainless 316 is a highly corrosion-resistant grade of stainless steel, and though more expensive than 18-8, it can be used to great effect in chlorine and salt water environments.
Harder than 18-8 stainless steel yet not quite as resistant to corrosion, meanwhile, is stainless 410.
The most common fastener material, steel can come plain, or with surface treatments, including chrome or zinc plating, or galvanization. More often than not, steel fasteners come in four grades – grade 2, grade 5, grade 8, and alloy steel, with the latter plated, in most cases at least, with blue-ish or yellow zinc coating.
How do you determine bolt grade and material selection in steel fasteners?
Look for the manufacturer’s stamp or mark, as well as a marking on the head. This tends to show what grade of bolt you’re dealing with, with some of the most common being three radial lines, six radial lines, or even no markings at all.
Manufactured from a high strength steel alloy, alloy steel bolts and fasteners typically come un-plated. This means that, in terms of appearance, they have a black finish – and while they’re extremely strong, they can be brittle.
Similar to stainless steel, aluminium’s corrosion resistance is integral to the material. This means that any nicks or scratches are unlikely to affect its corrosion resistance. Soft fasteners made from this material are done so from a variety of alloys, with elements including silicon, iron, copper, zinc, or manganese. Silicon is used to increase melting point and strength for a product you can rely on.
Polished for appearance, these fasteners are chrome-plated. This allows for a similar resistance to corrosion as zing plating.
What about downsides, though? Chrome can be expensive, but it’ll certainly give that project – whether it’s a car, boat, or motorbike – a professional finish.
Finally, silicon bronze is another key material for fasteners – but how does it fare?
More often than not, silicon is known simply as bronze. An alloy manufactured mostly from tin and copper with a small addition of silicon, this component can be used to great effect in marine environments, such as during the construction of a wooden boat. This is due to its excellent corrosion-resistance and high strength. Drawbacks include its high cost, but for the right project, silicon bronze will prove itself as the right variety of fastener for you.