A closure head is a component used to seal the ends of containers, isolating the internal and external media, also known as an end cover. The closure heads for cylindrical containers are typically rotating shells. They can be classified by the shape of their surface into convex, conical, flat, and composite types. A convex closure head refers to one with an outwardly convex outer surface, such as hemispherical, elliptical, dish-shaped, and seamless spherical types. Some gas cylinders use a composite bottom closure head with an inward-facing convex shape, which ensures both strength and meets safety requirements for use.