Different bolt grades are used in different contexts and applications across construction, manufacturing, and a range of other industries. Bolts are fasteners which are almost always made from steel, with external threads allowing them to be fastened to other materials without a pre-drilled hole. The bolt is inserted to fasten two materials together, using a nut screwed onto the end to hold it securely in place.
Bolt grades tell us both the material and the strength of the bolt. The higher the bolt grade, the higher the tensile strength of the bolt. What this means is that, the higher the grade number, the higher the amount of pressure, or weight, the bolt can withstand before it breaks.
Here’s a simple breakdown of some of the most common bolt grades which you might come across, as well as what they should be used for.
Grade 4.6
Grade 4.6 bolts are the lowest strength bolts that are readily available. This is because they have a very low carbon content, which makes their tensile strength lower. Grade 4.6 bolts have a minimum tensile strength of 400 MPa, alongside a minimum yield strength of 240MPa. This means that Grade 4.6 volts are suitable for a wide range of applications.
Grade 4.6 bolts, or sometimes 4.8 bolts, are best used in projects which don’t need a lot of strength and don’t come under any real stress or impact. They are a good fit for low impact DIY jobs around the house.
Grade 5.6 and 6.6
Grade 5.6 and 6.6 bolts are slightly stronger than 4.6 or 4.8 bolts, but still have a relatively low tensile strength. This low tensile strength gives 5.6 and 6.6 bolts another useful property though, as it means they are more flexible and malleable than higher grade bolts. This is particularly useful in projects which might be exposed to extreme weather and temperature fluctuations, as the bolts can bend and move with changing heat without just breaking. 5.6 grade bolts are great for applications that require a medium strength but lower hardness so that the steel can be put under stress and manipulated whilst being installed.
Grade 5.6 and 6.6 bolts are also easier to install than higher grade bolts as they can also be more easily manipulated without breaking.
Grade 8.8
Grade 8.8 bolts, and all bolts which are graded higher than this, are considered high tensile bolts, also sometimes referred to as structural grade bolts. This medium carbon steel bolt is heat treated.
Grade 8.8 bolts are the most commonly used of all bolts, as they offer a nice middle ground of strength, suitable for lots of different purposes.
Grade 10.9
Grade 10.9 bolts are most commonly used in car manufacturing due to their strength, durability and reliability. This high tensile grade screw has a tensile strength of up to 1040 minimum and a 940MPa yield strength minimum. They are particularly applicable for engine parts and similar components.
Grade 12.9
Grade 12.9 bolts are even stronger, made of an extremely strong steel with very high levels of carbon. Grade 12.9 bolts are often used in engines as they can withstand so much force and pressure. They are also commonly used in military vehicles and planes as they have to be so strong and reliable whilst withstanding a lot of weight.
Grade 14.9
Grade 14.9 bolts are the strongest, most durable bolts available, and are mainly used in construction.
For more information or advice on which bolt grade is right for your needs, get in touch with our team of experts at Confast.