The simplest switch has two pieces of metal called “contacts”, which form a loop when the two contacts are in contact, and the current is open when the two contacts are not in contact. The choice of contact metal needs to consider the degree of corrosion resistance, because most metals will form insulating oxides after oxidation, making the contact unable to work properly. The selection of contact metal also needs to consider its conductivity, hardness, mechanical strength, cost and toxicity and other factors. Corrosion-resistant metals are sometimes plating on the contacts. It is generally plated on the contact surface of the contact point to avoid affecting its performance due to oxides. Sometimes non-metallic conductive materials, such as conductive plastics, are also used in the contact surface. In addition to the contact, there will also be movable parts to make the contact on or not on, the switch can be divided into lever switch (Toggle switch), key switch, boat switch (Rocker switch), etc. according to the different moving parts, and the movable parts can also be other types of mechanical connecting rods.