Twist-on wire connectors are used to fasten two or more electrical conductors together. They are a type of electrical connector.
Twist-on wire connectors are also known as wire nuts ("Wire-Nut" is a registered trademark of Ideal Industries[1]) or cone or thimble connectors. Marrette or Marr connectors 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. Twist-on wire connectors are intended to be installed by hand only, and may include molded grooves or blades intended to assist in hand installation. Hex tips or hex-like wings are commonly molded into higher-quality connectors that allow them to be installed with a common nut driver.
Twist-on wire connectors are commonly color-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.
Twist-on wire connectors are not generally recommended for use with aluminum wire[2]; however, Ideal Industries makes a purple-colored Wire Nuttm that is listed for such use.[3] Also, most connectors are not rated for wet use (such as exposed outdoors), a special gel-filled connector must be used in this circumstance.