Banana plug, consisting of a cylindrical metal pin about 20 mm 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 back end of the banana plug is a color coded plastic insulator that may be red or black.

The back end of the plug has a hole that accepts a length of flexible insulated equipment wire. The wire will get secure in place by tightening the side screw. An insulating plastic cover is usually fitted over this end.
Sold in pairs or equal numbers of red and black.