Save money--double ended drill bit size 1/4 inch,5/16 inch only one bit,Equivalent to you owning two drills,Both ends offer extreme lifetime. Wide Applications --Dry Diamond drill bits are worked great for dry drilling holes through hard porcelain tile, ceramics,bathroom tile, granite & marble, masonry, concrete, glass, hard plastic with ease. Using water could prolong the lifetime Size --2pcs/pack,1/4" 5/16“(6-8mm), diamond height 10mm, total length 80mm,hex shank diamond drill bit， High Performance --Wax inside the drill bit helpful for Cooling and Lubrication,can be used without water to increase life Machine --Suitable for any electric drill,hand drill,Bench Drill, When use Angle Grinder,please install angle grinder drill chuck.