 Although his book did not elaborate on the trigger mechanism, it does mention the use of steel wheels as the trigger mechanism.The earliest illustration and description of the "steel wheel" mechanism was the "Binglu" of 1606.According to it, the steel wheel trigger mechanism utilized a pin release, dropping weights, cords and axles that worked to rotate a spinning "steel wheel" that rotated against a piece of flint to provide sparks that ignited the mines' fuses underground.