These 7/8" diameter, extra-fine grit, Garnet discs are manufactured with the grit resin-bonded onto one side of thin, flexible, plastic-backed discs. (Garnet is a natural mineral which is slightly less aggressive than Aluminum oxide.  Recommended for general use and with acrylics and gold.) These thin, flexible, plastic-backed discs reach into tight areas and conform to surface contours.  Since they are manufactured with the Moore Snap-on brass center, they need to be used with a Snap-on mandrel (sold separately).  Max. operating speed: 30,000rpm.  Sold in box of 200 discs.