This thing fits a 9V Battery Box (with the cover removed) to a standard breadboard. Because the breadboard is made of soft plastic, its dovetails do not provide a bomb-proof fit, but it's good for keeping your battery from flying around. The battery box makes a friction fit with the holder. Since it does not require the cover to be fitted, some cheaper, fatter 9V batteries can be used. Use it with your favorite prototype circuit, like the Atari Punk Console. Also see my breadboard speaker amplifier.