Twisted pair cables are used quite commonly in structured wiring systems. These cables contain eight wires within them, which are twisted pair-wise, to make four pairs of wires. The four twisted pairs of wires are mounted on a central cylindrical support and sheathed in a jacket. Twisted pair cables are used to a very large extent in residential and office wiring systems and in making Ethernet connections. There are different pairs of twisted pair cables in use. The most commonly used ones are the Cat 5 and the Cat 6 cables. An intermediate variety, Cat 5e, is also used a lot.