Robert Hall Originals :: Rock Shop :: Lapidary Supplies :: Silicon Carbide Wheels Our wheels are custom made in the US with the best high-purity silicon carbide. Green wheels are the cutting standard and have a soft bond to cut fast, stay cool and resist glazing. Black Wheels are a lower cost alternative with a medium bond and combine great cutting with long and dependable life. 1" arbor hole is brushed for 3/4", 5/8", 1/2" shafts.