Tip, ring, sleeve (TRS) connectors are electrical plugs and sockets that have three distinct contacts that are capable of conducting analog signals. These three conductive elements consist of the tip of the plug, a ring around the center of the plug, and the outer sleeve at the base. A number of connectors have used this same basic structure, though there are only three sizes that are commonly used. The TRS connector is the most common variant that uses this type of plug, though tip, sleeve (TS) and tip, ring, ring, sleeve (TRRS) versions also exist. Headphone cables that are designed to carry analog audio signals represent one of the most popular uses for the TRS connector, though these plugs have other uses as well.
The first TRS connectors were developed for use in early telephone switch boards, where they could be easily plugged and unplugged to route calls. For that reason, these connectors are sometimes referred to as phone plugs. Since these connectors make use of three electrical contacts, located on the tip, ring, and sleeve of the plug, the initialism, "TRS," was also coined to describe them.
Modern TRS connectors come in three basic sizes, each of which has a variety of uses. The largest commonly used TRS connector has a diameter of 0.25 inches (6.35 mm), and the smallest has a diameter of about 0.1 inches (2.5 mm). Many consumer electronics applications use a version of the TRS connector commonly known as the mini plug, which has a diameter of 0.125 inches (3.5 mm). When this type of connector is used with stereo headphones, the left audio channel is passed through the tip connection, the right channel through the ring connection, and the sleeve acts as a common ground. Other applications use TRS connectors to transmit balanced monaural signals by using the tip and ring contacts as positive and negative connections.
Aside from the basic TRS connector, a number of other plug and jack connectors share a very similar design. The TS connector is a variation that has only two electrical contacts, which makes it useful for transmitting unbalanced mono signals. Another variant is the TRRS connector, which has four contacts. These connectors are sometimes used with cellular phones and other similar devices, since they can be used to transmit audio to a headset, from a microphone, and also include some type of control signal. Other variants, some of which are designed for use with camcorders, can include even more contacts than a TRRS connector.