How to distinguish the material of long allen screw?

Sometimes when we look at the long allen screw, is not to see the material of the screw, especially the screw surface treatment, it is difficult to distinguish in the end is iron material or stainless steel, other material is better to distinguish, so how to distinguish its material?

By weight, copper > stainless steel > iron > aluminum > pure titanium. The density of stainless steel material is about the same as that of iron material. The long allen screw under the same specification has no difference in weight. But if it’s very light, it’s basically titanium and aluminum.

Stainless steel with iron material long allen screw, can distinguish through the magnet, but sometimes stainless steel material screw specification is relatively small, may contain some weak magnetic, will cause the screw will also be magnet to suck. This time can be distinguished by the stainless steel potion. If the titanium and aluminum screws are natural, they can be distinguished by looking at the surface. However, if the surface treatment is done, the surface can not be seen. In this case, it is necessary to detect the composition of the wire and judge what kind of screw is made by the composition of the wire.