Korner Weldcote Flap Discs Have Unique Design Where The Material Wraps Up Around The Edge Of The Flap Disc And Allows The User To Grind Aggressively Into “Korners”. Z-Prime Has Poly-Cotton Backing Which Allows Excellent Flexibility For Enhanced Life. Z-Prime Provides Cool Cutting With A Built-In Grinding Aid To Provide Cool Cutting With Light Pressure.