A closure head is a component used to seal the end of a container, isolating the internal and external media, also known as an end cap. The closure heads for cylindrical containers are typically revolving shells. They can be categorized 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 surface, which ensures strength while meeting safety requirements for use.