This battery holder can fit 4 AA 1.5V batteries, providing a total of 6 Volts (for Alkaline batteries since some rechargeable batteries may have the same size but different voltage).
The barrel jack plug fits most educational boards, including the Board of Education from Parallax and the Arduino microcontroller.
This unit comes by default in the Boe-Bot robotic kits so if you need a replacement for a 4 AA battery holder, this will be the right choice.