What's the difference between a bolt that can handle heavy duty motors and one that can't even hold a wooden shelf?

What's the difference between a bolt that can handle heavy duty motors and one that can't even hold a wooden shelf? 

The secret lies in what's known as "bolt grade," which is simply a measure of a bolt's strength and its ability to resist tensile stress before breaking.

 In the metric system, we see symbols like 8.8 or 10.9, where the first number indicates the maximum tensile strength, and the second number represents the percentage of yield strength. For example, a bolt rated 8.8 has a tensile strength of 800 MPa and a yield strength of 640 MPa, making it suitable for medium to heavy-duty applications. In the American system, symbols like Grade 2, Grade 5, or Grade 8 are used, and the higher the number, the stronger the bolt. Grade 8, for example, is made of heat-treated, high-carbon steel and is used in heavy machinery and vehicles.  Choosing the right screw pitch isn't a random matter; it can mean the difference between safety and danger, between success and failure in engineering projects. Therefore, understanding this rating is essential for anyone working in construction, industry, or even home maintenance.