Rose copper or brass

Generally, the conductive part is made by copper, because its high conductivity and difficulty in oxidation and corrosion in the air compares to iron, also it is cheaper than the better conductive silver, and the aluminum surface is easy to form a dense oxide film which is not good for conductivity.

The insulation part normally uses resin material, for example, phenolic resin or something else, rubber is also been used, but the hardness is not enough, plastic and ceramic are also been used, but firstly is heavy, secondly the process is relatively complex, and high in cost.