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 combined shapes. A convex closure head refers to one with an outwardly convex outer surface, such as hemispherical, elliptical, dish-shaped, and seamless spherical heads. Some gas cylinders use a combined bottom closure head with the convex surface inward, which ensures strength while also meeting safety requirements.