Special Reminding - These flute countersink drill bit set are machined from high speed steels and are available in 6 different diameter sizes. Size - 6mm(1/4''), 8mm(5/16''), 9mm(3/8''), 12mm(1/2''), 16mm(5/8''), 19mm(3/4'').Mutiple Application - Ideal for wooden planks,fiberboard,particle board,plywood,plastic,alumiumn board ,pcb board and more Premium Design - Great for Sinking 90 Degree Holes into Wood and Soft Metals Countersunk Screws and Fixings.Suitable for DIY, Home and General Building/Engineering Using.Mutiple Application - Ideal for wooden planks,fiberboard,particle board,plywood,plastic,alumiumn board ,pcb board and more.Sweet Tips - 1/4 hex shank countersinks are fine for a quick drill. They dont slip in drill chucks. You can make deep countersinks easily by setting the countersinks depth stop to allow the countersink to drill more deeply into the worksurface. Be sure to measure the size of your plug to be sure your countersinks body will make the right-size hole. IF you have any problem about the item,please first so that we can help you out.