Whats the difference between metric property classes and inch-series grades?
In the metric system, the strengths of different fasteners are broken down into property classes and each class uses the same numbering convention – a combination of two numbers X.Y. The first number represents the approximate tensile strength multiplied by 100 in metric units of MPa. The number following the decimal represents the percentage to multiply the tensile strength by to find the approximate yield strength. For example, for property class 12.9, the approximate tensile strength is 1200 MPa and the yield strength is approximately 90% of this value, or 0.9*1200 = 1080 MPa. The SAE grade numbers don’t employ a similar convention. The chart below details how the metric and inch-series grades match up.
