The SparkFun Fuse Breakout Kit comes with everything you need to assembly & use a glass capsule, inline fuse (ferrule type) for your project. The simple breakout design allows for a barrel jack and the option for a screw terminal to be used for (VIN) power input and a second screw terminal used for VOUT. Any 5mm x 20mm glass capsule fuse can be used with this kit depending on your project needs but we have been sure to include a 250VAC, 500mA one to get you started. Make sure to check out the related products and add additional fuse in your cart as a replacement for prototyping and testing.
Fuses are pretty simple, if current exceeds the rating of the fuse, the small filament inside the fuse heats up and breaks (like a light bulb burning out). The circuit is then broken and hopefully, your circuit is saved from molten destruction. For smaller loads, you may want to check out a PTC (aka resettable fuse). Depending on the PTC's spec, they can handle less current (500mA) but can be set and reset many times without doing harm to your system. Since this is a kit, some soldering and assembly will be required.
Note: The PCB was designed for DC power. It was not designed for AC power. Make sure that you are using the fuse breakout on the DC side for protection.