DC Power Screw Male Jack adapter - 2.1mm plug. Other than many general usage, its easy to plug battery to Arduino board via this jack.

If you need to connect a battery pack or wired power supply to a board that has a DC jack - this adapter will come in very handy!

There is a 2.1mm DC plug on one end, and a screw terminal block on the other.

The terminals are labeled with positive/negative assuming a positive-tip configuration (which is the most common)