The main characteristic of stud earrings is the appearance of floating on the ear or earlobe without a visible (from the front) point of connection. Studs are invariably constructed on the end of a post, which penetrates straight through the ear or earlobe. The post is held in place by a removable friction back or "clutch" (also known as a butterfly scroll). A stud earring features a gemstone or other ornament mounted on a narrow post that passes through a piercing in the ear or earlobe, and is held in place by a fixture on the other side. Studs commonly come in the form of solitaire diamonds. Some stud earrings are constructed so that the post is threaded, allowing a "screw back" to hold the earring in place securely, which is useful in preventing the loss of expensive earrings containing precious stones, or made of precious metals.