This power jack is designed to fit 2.1mm power plugs snugly and securely. Perfect for adding a power connector to your project. We went for the more expensive "thin pin" type which snap into breadboards or perfboards. They will work where "thick pin" types go also, just need a little more solder to fill up the larger pads.

The pin at the end of the jack is the positive pin, the pin in the 'middle' of the jack is the negative pin, and the pin to the 'side' of the jack is switched: when a plug is inserted it floats, when not inserted it is connected to the negative pin.