This adapter allows you to plug a (male) barrel jack connector to bare wires. One end has screw terminals and the other has a 5.5mm×2.1mm, center-positive (female) barrel jack. If you have a power supply or battery pack with a barrel jack and want to plug it into a breadboard or perfboard this adapter provides the simplest solution.This adapter allows you to connect a DC power supply (e.g., wall wart) to a board or project without a barrel jack connector. It's quite common to run into the problem of battery and power supply connectors not matching the jacks on electronic devices, thus this adapter helps make a secure connection from the plug of our power supplies to wires that we can use to power our projects.This adapter has a 2.1mm DC barrel jack (female) on one end, and a screw terminal block on the other. The terminals are labeled with positive/negative assuming a center-positive configuration, which is the most common.