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