At the bottom of the body is an assembly called the bridge, a large metal assembly into which one end of the strings are fitted. On some designs, the strings are fasted through the back of the body into the bridge; on others, the strings fit into the front side of the bridge. In some basses, there is a cavity inside the back of the body that contains the electrical parts of the bass. These are usually called active basses. The bridge often has adjustments that allow the height of the strings to be changed. Other components found on the body include one or more pickups and various knobs or switches that control the sound of the bass.