... . Sand disc Specifications1) Sizes: 4", 4.5", 5", 6", 7" 2) Fiber thick: 0.6, 0.7, 0.8mm 3) Grain: alumina ... #, 24#, 36#, 40#, 60#, 80#, 100#, 120#, 220#...400#5) Fiber thickness: 0.6mm, 0.7mm, 0.8mm6) Center: flat, depressed7 ... -resistant, long life, stable performanceOne hole depressed center aluminum oxide fiber disc for metal sanding disc