Bolts are fasteners usually made of stainless steel used to hold two objects together. Although bolts can be used in simple DIY projects at home, they are also commonly used in the making of vehicles, airplanes and marine machines. With various bolts on the market, selecting the right bolt type and the appropriate bolt grade for your project is very important.

Pattern of nuts for the bolts
credit: Jarwis/iStock/GettyImages
Types of Bolts

Stainless Steel

Stainless steel is usually the material of choice when making bolts because it is corrosion resistant therefore the bolts will last much longer. Corrosion, or commonly known as rust, will not be a concern and therefore the bolts will have a longer lifespan. Another benefit to using stainless steel is its non-magnetic. The element used within the bolt to help prevent corrosion is called Chromium and the higher the amount of Chromium used in the bolt, the more it will be resistant against rust.

A2 vs. A4 Bolts

A2 or A4 bolts are often grouped with numbers such as -70. These numbers usually signify the bolts tensile strength. The tensile strength represents the load that this particular bolt can hold before the material breaks, cracks or becomes defective. A2 bolts are often used when manufacturing vehicles or vehicles parts and A4 bolts are best for environments where corrosion is more likely to happen such as marine equipment or exhausts.

When it comes to vehicles A2 bolts are sufficient because the bolts needed do not require as much chromium. Vehicles are also light in comparison to other machinery which is why the lower tensile strength and yield strength are acceptable. It is unnecessary to build vehicles using A4 bolts because A2 bolts will generally outlive the vehicle already making the more expensive bolt useless. A2 bolts are not made to hold heavy machinery or any other potential heavy load which is where A4 bolts become necessary.

Bolt Grades

Bolts are assigned various grades and these grades are usually stamped on the bolt's head for easy referral. If there are zero markings on the bolt head, it is usually because the bolt in question is of the lowest grade. A bolt with a low grade two is often manufactured with low or medium carbon steel. This bolt would not hold a high tensile or yield strength meaning it could not withstand much stress or pressure before the bolt becomes compromised. There are other grades such as five (with the radial lines of the head) and grade eight (with six radial lines on the head). These bolts are made with higher quality materials such as medium carbon steel that are also tempered and quenched making them stronger. As the bolt grades rise is number, the strength that the bolt can withstand also grows as well.