Threaded Bar Metric 8.8 High Tensile In 1 Metre Lengths

Two grades of bolt are commonly used. These are grade 4.6 and 8.8.

The first digit relates to the ultimate strength of the material, whilst the second is the ratio of yield stress to ultimate strength.

Thus grade 4.6 bolts have an ultimate material strength of 400N/mm2 and the yield (or proof) stress is 60% of the ultimate strength.

Similarly grade 8.8 bolts have an ultimate strength of 800 N/mm2 and a ratio of yield / proof stress to ultimate strength of 80%.