Back-up pad provides extra support to a right angle grinder, enabling the use of heavier pressure when sanding Works with 9" diameter Norton A290 hook-and-loop discs for Porter Cable drywall sander, model 7800 (sold separately) Hook-and-loop abrasive discs can be removed and reattached multiple times with no loss of adhesion, which can increase abrasive disc life Fits a variety of 9" discs sanding systems Works with a 9" hook and loop disc Allows quick disc changes