This is a tiny little circuit board that can protect your precious projects, kits or any other electronic device which could be zapped if you connect power up the wrong way! This board has a power input end and an output end marked on the silkscreen and in between is a DMP205U-7 P channel MOSFET and a couple of decoupling capacitors. If you connect power to this board the wrong way around at the input absolutely no power passes to the output and the circuitboard itself, and the attached project, is unharmed. Correctly connecting the board the right way allows the vital voltage and current to flow correctly to your project. The board can handle up to 20V DC and a maximum continuous current of 4.3A. I built this little board originally as I had some expensive kit built altimeters which had no polarity protection and I managed to break one in the field. These boards are small enough (6.25mm wide) that you could wire them in the middle of a power cable and heatshrink over it and barely notice them. As such I supply them with the header pins no soldered into place for if you want to directly wire to the board. If you wire the headers into each end you can of course use this clipped into a breadboard or into a header socket. I've included an M2 compatible mount hole as well for if you want to bolt this to an avionics sled or experiment board etc. Finally these are really efficient, there's no voltage drop and they consume a tiny (undetectable on my benchtop power supply) amount of current when powered up on their own.