Excellent question. Checking your bolt rating is a critical step for ensuring safety and proper function in any application, from automotive work to structural projects. Here’s a comprehensive guide on how to do it.
You check your bolt rating by looking for markings on the bolt head. These markings indicate the property class or grade, which defines the bolt’s strength (tensile and yield strength). No markings usually mean a lower-grade bolt.
The system differs between Metric (ISO) and Imperial (SAE Grade) bolts.
A. For Metric Bolts (e.g., M10, M12) Look for a number like 4.6, 5.8, 8.8, 10.9, or 12.9. This is the Property Class. How to read it: The number before the decimal point multiplied by 100 gives the minimum tensile strength in MPa (e.g., 8.8 = 800 MPa). The ratio of the numbers gives the yield strength (e.g., 8.8: yield strength = 0.8 x 800 MPa = 640 MPa