Heavy duty zirconium grain, designed for high pressure applicationsDurable polyester backing for reduced edge wear and long lifeHigh density flap discs contain approximately 40% more material than conventional, regular density flap discsContaminant Free (Fe + Cl + S < 0.1%)Type 27, Flap discs are constructed by layering coated abrasive flaps so they wear away and expose new, sharp grainFlap discs increase productivity and reduce total grinding and finishing costs by grinding, blending & finishing in 1 stepFiberglass backings will wear uniformly with abrasive cloth and will not splinter or smear on the workpieceFiberglass backed flap discs are designed for a lighter, quieter operation