These laps are absolutely flat and parallel to meet the most exacting faceting requirements. The diamond grit is plated straight on to the steel disc, whereas some economically priced laps have a disc glued onto a master lap. Manufacturing this way prevents any chance of fluctuations in the surface. This makes this disc ideal for cutting competition quality gems.
Additionally, these discs have a corrosion resistent copper undercoating. A 1/2" arbor hole is standard.