A closure head is a component used to seal the end of a container, isolating its internal and external media, also known as an end cap. The closure heads for cylindrical containers are typically rotatable 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 a 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 both strength and safety for use.