The banana plugs will connect up to 3.5mm diameter speaker wire. speaker cable can be connected easily through the top of the banana plug using a screw to hold the speaker wire in place.
the overall length of the banana plug is 40mm and the pin is 14mm long. the pin is 4mm in diameter (like quoted in the title).
the plugs can be stacked into the side of one another if required.
all the banana plugs are colour coded so you can attach the negative wire (black) to the black banana plug and the positive wire (red) to the red banana plug.