Blue Zirconia Alumina Sanding Discs are ideal for use with platinum, but will work well on gold and silver. These discs are resin-backed for superior durability and aggressively cut and grind metals with a uniform file-like finish. Last up to three times longer than conventional abrasives. Comes supplied in 3/4" and 7/8" diameters with snap-on centers. The brass-centered holes reduce vibration as they work. For snap-On Discs, use Gesswein's Snap-on Mandrel. Made in USA.