Fuses are mainly composed of 3 parts of the melt, shell and support, in which the melt is the key element to control the fusing characteristics. The material, size and shape of the melt determine the fusing characteristics. Melt materials are divided into two categories: low melting point and high melting point. Low melting point materials such as lead and alloy, the melting point is low and easy to fuse, because of its large resistivity, it is made into a larger cross-sectional size of the melt, the metal vapor produced more, only applicable to the low breaking capacity of the fuse. High melting point materials such as copper, silver, its high melting point, not easy to fuse, but because of its low resistivity, can be made less than the low melting point of the melt smaller cross-sectional size, the metal vapor produced when the fuse is small, suitable for high breaking capacity of the fuse. The shape of the melt is divided into two types: Filiform and banded. Changing the shape of the variable cross-section can significantly change the fuse's fusing characteristics. Fuses have a variety of different fusing characteristics, which can be applied to different types of protection objects.