According to ISO 898-1, carbon steel and alloy steel bolts are marked with a two-digit system called the property class: 4.6, 5.6, 8.8, 10.9, 12.9 and so on.
How to Read the Numbers?
The first number indicates one hundredth of the nominal tensile strength in MPa: for class 8.8, 8 × 100 = 800 MPa. The second number gives the ratio of yield to tensile strength: for 8.8, 0.8 × 800 = 640 MPa yield strength.
Which Grade Is Used Where?
Class 8.8 is the general-purpose high-strength standard for machinery and steel construction. 10.9 is used in preloaded structural connections (such as EN 14399-4 / DIN 6914) and heavily loaded joints. 12.9 is common in dies, machine elements and socket head cap screws.
As the property class increases, torque values, hardness ranges and coating selection also change; bolt class must therefore be evaluated together with nut and washer classes in joint design.
All bolts in our production range are shipped with mechanical properties certified to ISO 898-1.