A set of switches being installed with wire nuts (orange and green) used to make connections. Wire-Nut[1] is a registered trademark of Ideal Industries for a product technically known as a twist-on wire connector. These connectors are used to fasten two or more electrical conductors together. Twist-on wire connectors are also known as a cone or thimble connectors. Marrette or Marr connector are two other trade names for such connectors. In the UK, they were made out of ceramic and sold under the brand "Scru-it". Twist-on wire connectors are available in a variety of sizes and shapes and are typically made from plastic, with a tapered, conducting metal coiled insert that threads onto the wires to hold the wires secure. Cheaper varieties often didn't include the metal coil, relying instead on molded plastic threads. Twist-on wire connectors are commonly colour-coded to indicate the nut's size (and hence, its wire capacity). They are commonly used as an alternative to terminal blocks or soldering conductors together because they are cleaner, faster, and allow subsequent removal for future rework. In the past, twist-on wire connectors were occasionally made of ceramic with molded threads and no internal metal coil. In many areas, this style of twist-on wire connector is no longer approved by the regulatory authorities for ordinary use, however, they may still be required in certain specific high temperature conditions. Wire nuts are widely used in America, but have not been permitted on 240v mains installations since the 1950s in Britain.[citation needed] [edit] A variation on the twist-on wire connector A new variation has, unlike ordinary twist-on wire connectors, a portion that threads onto the wires by means of a metal spring enclosed within a rigid steel canister. The spring develops very large forces on the contained wires, cutting into the wires and providing a more-secure connection. The metal can is insulated by means of a resilient plastic over-cover which is provided with two wings to allow easier turning by hand. Like ordinary twist-on wire connectors, these connectors come in several colors indicating their size with yellow being the smallest, then red, grey, and blue. Unlike conventional twist-on wire connectors, these connectors permit but do not require that the joined wires be pre-twisted before installation of the connector. Older versions of these connectors could only be used once; they twisted on but the spring action did not allow them to be twisted off again without the user first crimping (and thus destroying) the connector. More-recent versions can be removed in the same fashion as ordinary twist-on wire connector: simply unscrew them. [edit] See also Screw terminal [edit] References This article does not cite any references or sources. (February 2008) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.