The Optimized Surface Preparation (OSP) system maximizes the performance of every individual phase of the process, with each step optimized to work perfectly with all the other steps. Mirka’s OSP abrasives are clearly marked with numbers telling which disc or strip should be used for each step. Number 1 is used for paint removal, number 2 for feather edge, number 3 for preparing the repaired area for primer by reducing scratches and expanding the feather edge and number 4 for finalizing the sanding.