Banana plugs are little cylindrical plugs that allow a single wire connection to a device for electronic testing or electrical purposes. Banana plugs usually have a copper plating to improve conductivity when placed into a socket. The distinctive bulge in the plug houses a spring that, when inserted into a socket, presses outwards to ensure a secure connection. The plug takes its name from the shape of this prong, which reminds many people of a straightened out banana.
Banana plugs are a great alternative to using bare wire for your connections as they provide vastly improved connections compared to bare wire. Used as speaker wire, as banana plugs offer a superb connection with high sound quality. The term 'banana plug' or 'banana jack' refers to the 4mm version. However, there are 3mm and 2mm variations and these are called 'mini-bananas', but they cannot be used interchangeably.