General description High quality diamond powder lapidary drill bits, precise and durable. Ideal for drilling holes in materials for jewelry, ceramics, jade, agate, glass, amber, and semiconductors. Technical specifications Size: 1.9-2mm Quantity: 20 pieces per pack Usage The higher the speed of the drilling machine, the better the effect of the drill bits. Recommended speed: 2000 rpm for optimal performance. Use cold water during the drilling operation to enhance the drilling process. For prolonged use, if the drill bit becomes dull, you can cut the top slightly with pliers to restore sharpness.