High quality diamond powder lapidary drill bits, precise and durable. Idea for drilling holes in materials for jewelry, ceramics, jade, agate, glass, amber and semiconductors, etc. The higher the speed of the drilling machine, the better the effect of the drill bits. The speed of the drilling machine should be reached to 2000 rpm when you use our drill bits to drill holes. Please use cold water during the drilling operation. If you use the drill bit for many times, it will not be very sharp with the first use. You could cut the top a little with pliers, it will become sharp again.