【Size】Totall 2pcs dry diamond core drill bits. Diameter 6mm 1/4 Inch, diamond length 10mm,Hex Shank. Multi-purpose drilling for granite & marble, masonry, concrete, tile/ceramic, stone. 【Highly advanced technology】By adopting high-end vacuum brazing technology, the diamond and the substrate bond closely and the service life is long and reliable, which is the ideal choice for your drilling work. 【Contains cooling wax】 By using cooling wax,can be drilled directly dry without adding water, which extends the service life and at the same time allows you to work more comfortably and quickly.Please use with water when drilling granite. 【Excellent Finish】Diamond is dense and delicate, less debris when drilling, with smooth and perfect drilling effect. 【Applicable machines:】Suitable for general hand drill (plug-in model), table drill. Generally, the rotational speed of electric drill is 2000-5000RPM, the faster the better, the slower the life is shorter.