GP PRO System used and recommended by our technicians. It is perfect for scratch removal, water marks, lime scale, grinder splatter damage, graffiti damage, edge finishing and a variety of other applications.This discs are constructed from top grade nano aluminium oxides gives you best cut against any glass surface. With a hook and loop Velour backing to be used with any 4.5" 115mm Velcro Backing Pad. GP-PRO abrasive system uses a four step process depending on the depth of scratched glass.*GP150 (extra coarse) *GP100 (medium coarse)*GP50 (fine) *GP20 (ultra fine) Ultra Fine GP20 used for visible hairline scratches (that cannot be felt with finger nail) and heavy hard water removal on glass surface that cannot be remove with polishing disc. Required Polishing Process (with cerium oxide or glass polishing compound )