o These 400 grade discs are used for primer sanding.o Better cutting and long lasting abrasive disc for primer sandingo Reliable dust-extraction and reduced loading due to multi-hole patternReliable dust-extraction and reduced loading due to multi-hole patterno Engineered ceramic mineral blend provides best-in-class performance using exactly the right balance of ceramic grain and premium aluminum oxideo Anti-loading coating improves abrasive life while upgraded resins improve durability and finisho Suggested backup pad PN05551 and interface pad PN05777