Electroplated (nickel bonded) diamond grinding wheels, with plastic center core. Made with the highest quality diamonds for longer grinding life, clean and faster cutting. Can be used on all conventional grinders made today. All wheels have a 1 inch Diameter arbor and include bushing to accommodate 3/4 inch, 5/8 inch and 1/2 inch arbors. The plastic hubs are lighter and can be used on less powerful grinding machines.