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