This instructable works on the principle that when flint is dragged on the pavement it will leave behind a shower of sparks. So where can we find a flint-like material up for the job? Your local big-box retailer! I picked up some Razor X spark cartridges for this project. They are meant to be mounted on the back of a Spark SK8 board. As I don't ride skateboards, I needed to figure out a way to attach this to my bicycle.