USB cables are used to connect devices that use the USB standard, such as computers and peripherals. The cables are usually made of copper wire and have a standard construction of four twisted pairs, each pair consisting of two insulated conductors. The cables are also often shielded to protect them from interference from external sources. The most common type of USB cable is the Type-A cable, which is used to connect devices such as printers and scanners to a computer. Type-B cables are used to connect devices such as digital cameras and camcorders to a computer. Other types of USB cables include mini and micro cables, which are used to connect smaller devices such as smartphones and MP3 players to a computer.