Metal caps are small, often circular pieces made from various metals, commonly used to seal containers like bottles and jars. They help preserve the contents by preventing air and contaminants from entering. Metal caps can be found on products such as beverages, food items, and even some pharmaceuticals. These caps come in different designs, including screw-on and snap-on types, and can be lined with materials to enhance sealing. They are often recyclable, making them an environmentally friendly option. Common metals used for caps include aluminum and steel, which provide durability and protection for the products inside.