Zumba, Good question. I do not know myself, I'm sure somebody out there will tell us. I'm going to take a guess. Single layer plated CBN or diamond??? They are not dressed to size and shape after finishing in their mfg. process, only cleaned. We used them to finish the roots on turbine blades. As long as the wheels were high pressure cleaned with the coolant, they had long life for fairly small diameter wheels.