Specially designed ABS plastic backing can easily be trimmed away to expose more abrasive material.Unique design is ideal for hand rail and fillet weld applications.High performance zirconium grain for a wide variety of applications.Contaminant Free (Fe + Cl + S < 0.1%).Type 27., Only the TrimBack??????????line of flap discs are able to be trimmed to expose more abrasive overhang.Never trim beyond the maximum trim line (more than 1/4") or the ridged edge of the backing TrimBack??????????plastic backing.Always mount a TrimBack??????????flap disc on a properly guarded right angle grinder.To properly trim a TrimBack??????????flap disc, apply the plastic backing to a secured metal workpiece while the grinder is running.TrimBack??????????is also available in a Type 29 Shape.