Spiral grinding: In this technique, the spirals are ground from a round rod. These bits are extremely precise and are used for quality work. You can often tell a ground bit by its silver colouring.
Rolling technique: The (hot) rolling technique is used to manufacture simpler bits. A round rod is pressed through a mould, which gives the bit its helical shape. These bits are more suitable for coarser work. You can often tell rolled bits by their black colouring.