GP13402 GP-PRO50 FINE Grade Sanding Disc for Glass, Silicon Carbide Abrasive Disc / 4.5-Inch (Pack of 10) Discs diameter: 4.5 inch / Pack of 10 Discs Constructed from top grade silicon carbide, with blue velour backing for use with any Velcro backing pad GP-PRO50 Fine Grade Pre-polish disc ideal for removing abrasive marks left by GP100, for hard water stain, lime scale or for light scratches removal Recommended to use with electric rotary device ( drill, polishing machine ) at about 1500-2000rpm. For best results final polishing process is required. Please check detailed product description for more information's.