All three blades come attached, with a scoring mark to show where to seperate them. Use needle nose pliers to clamp along the score mark, and apply light pressure to blade, it should snap easily.
B Bradley, vineyard operator from NC wrote (June 29, 2011):
While they should be easily separated along the score. It is not as easy as they say. They are brittle and can break diagonally. Pretty expensive waste when they could be cut to start with