A. A banana connector (commonly banana plug for the male, banana jack or banana socket for the female) is a single-wire (one conductor) electrical connector used for joining wires to equipment. The plugs are frequently used to terminate patch cords for electronic test equipment. They are also often used as the plugs on the cables connecting the amplifier to the loudspeakers in hi-fi sound systems.
The plug consists of a cylindrical metal pin about 25 mm (one inch) long, with a diameter of 4 mm, which can be inserted into a matching 4 mm socket to make an electrical contact. The pin has one or more lengthwise springs that bulge outwards slightly. These press against the sides of the socket, improving the electrical contact and preventing the pin from falling out. The curved profile of these springs is probably the origin of the name "banana plug". The other end of the plug has a lug connector to which a length of flexible insulated equipment wire can be attached, which is either screwed, soldered, or crimped into place. An insulating plastic cover is usually fitted over this end.
The rear end of a 4 mm plug often has a 4 mm hole drilled in it, either transversely or axially, to accept the pin of another 4 mm plug. This type is called a stackable 4 mm plug.
For high voltage use, a special sheathed version of the banana plug and socket is used. This version has an insulating sheath around both the male and female connectors to avoid accidental contact. The sheathed male plug will not work with an unsheathed female socket, but an unsheathed male plug will fit a sheathed female socket.
Individual banana plugs and jacks are commonly color-coded red and black but are available in a wide variety of colors. Dual banana plugs are usually black with some physical feature such as a molded ridge marked "Gnd" indicating the relative polarity of the two plugs.
Besides plugging into specific banana jacks, banana plugs may plug into five-way or universal binding posts on audio equipment.