The tensile strength of screw is also called strength limit, which refers to the maximum stress value of material before breaking.
When the steel yield to a certain extent, due to the rearrangement of the internal grains, its deformation resistance ability is improved again. At this time, although the deformation develops rapidly, it can only increase with the increase of stress until the stress reaches the maximum value.
After that, the steel's ability to resist deformation is obviously reduced, and a large plastic deformation occurs at the weakest point, where the cross section of the specimen shrinks rapidly and necks down until fracture failure. The maximum stress value of steel before tensile fracture is called strength limit or tensile hardness.
