For use with 4" backer pad. Resin-bonded to resist heat and humidity for longer life. Gator fiber discs are designed to be used on angle grinders with a backer pad for aggressive sanding of metal, fiberglass and painted surfaces. FIBER DISC Dia In=4-1/2 Grit=120 ''GATOR-FINISHING'' 7/8" ROUND ARBOR ALUMINUM OXIDE