Proxxon Tungsten Carbide Micro Drills Made of tough, resilient tungsten carbide. With ideal cutting angle of 6 degrees, used for drilling glass, semi-precious stones, porcelain, ceramics, marble and other hard stones. Hard stones are subdivided according to the degree of hardness from 1-10. Tungsten carbide can be used up to a hardness degree of 6. Drilling hard stones with a hardness degree of more than 6 calls for the use of diamond tools. Shank size is 3.0mm, sold in packs of 2.