The head refers to the element used to close the end of the container to isolate the internal and external media, also known as the end cap. The head of the cylindrical container is generally a revolving shell. According to the shape of the head surface, it can be divided into convex, conical, flat and combined. Convex head refers to the head whose outer surface is convex, such as hemispherical, elliptical, dish-shaped and spherical head without folding. Some gas cylinders use a combination bottom head with a convex inward face, which can not only ensure the strength, but also meet the needs of safe use.