What Do The Markings On The Bolt Heads Mean?
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When it comes to the most commonly used bolt performance grades today, the metric system set by ISO is the go-to standard. These grades are represented by two numbers separated by a dot, often found on the bolt head or nut. Some of the more popular grades include 8.8, 10.9, and 12.9. If you multiply the first number by 100, you'll get an approximate minimum tensile strength in MPa. The second number, when multiplied by 10, gives you an estimate of the yield strength as a percentage of the tensile strength. For instance, a grade 8.8 bolt has a tensile strength of around 800 MPa and a yield strength of approximately 640 MPa (80% of 800).
Now, when it comes to stainless steel bolts, you might see markings like A2 or A4. A2 refers to 304 stainless steel, while A4 corresponds to 316 stainless steel. Following these letters, there’s a number that indicates the tensile strength, which varies based on the specific bolt's strength. For example, a “70†would mean the tensile strength equals 700 MPa for standard stainless steel bolts. Both 304 and 316 offer excellent corrosion resistance, but 316 is superior and ideal for environments with higher demands.
Sometimes, you’ll notice that certain bolts lack any visible markings. This typically indicates that the bolt’s performance level is relatively low, such as grades 4.8 or 5.8, which are usually unmarked.
At Aozhan Fasteners, we’re proud to be a comprehensive service provider specializing in the production, processing, and trade of screws, nuts, and other fastener products. Over the past decade, we’ve focused heavily on creating custom-shaped bolts and screws tailored to our clients’ needs. We welcome both drawing design orders and OEM/ODM projects, offering technical support and after-sales services. Our mission is to serve major dealers, wholesalers, and industrial companies worldwide, providing them with high-quality fasteners and customized non-standard components. We operate on the principle of "quality first, innovation drives growth, and service ensures success." Your trust in us is our greatest reward, and we aim to become your trusted one-stop fastener supplier and long-term partner. Whether you need bolts or other fastener solutions, Aozhan Fasteners is here to assist you fully. Please feel free to reach out to us—we’re eager to collaborate with you and build a brighter future together!