Klingspor is a premium manufacturer of abrasive products for hand tools.  Their SMT flap discs (aka mop discs) are engineered for intensive grinding  tasks, and are of industrial quality. This original series are somewhat less costly than the Klingspor Titan Flap Disc series and selected features are as follows:

• Arbor.  All versions (except 1) have the standard 7/8″ open arbor for nut-mounting.
• Sizes.  All versions come in 4-½” diameter, with selected models also available in 6″ and 7″.
• Quality Classes.  3 grades available as follows:
  • Special.  High performance and service life in the most demanding applications.
  • Supra.  Reliable performance with a superior blend of life and aggression.
  • Extra.  Professional quality at a more affordable price for operators who do not use them continuously.
• Abrasive choice.  All common industrial abrasives available including alumina zirconia, ceramic, and aluminum oxide.