These gray, 270 grit (50 micron) 3M™ Micro-Finishing Film belts have a high-strength polyester film backing and the aluminum oxide abrasive is resin bonded for excellent durability.  Ideal for mold repair, jewelry making, watch repair, and medical devices. This material works well on both metal and plastic.  One belt comes installed on the Sanding Detailer Multi-Functional Sanding Tools.  Sold in packages of 10.  These belts are color-coded which allows you to quickly select the right grit for your task.