60mm best Nickel Electroplated Diamond Donut Burs Point Bits

Nickel electroplated diamond grit 80# 240# and 320# donuts burs. Designed for to grind simple and quick a donut. On the top are holes which allows water flow trough to keep the working surface well and properly lubricated. Step best one, drill the middle hole, step 2 use the donuts tool, the middle hole who you drill before will you guide.Shank size 6mm, best in use with drill press.