Backup Pad for Resin Fiber Disc Specifications Diameter Size 4”, 4-1/2”, 5”, 7”, 9” Backup Pad for PSA and Hook & Loop Specifications Dia. Size x Vacuum Hole 5" x no-hole 5" x 5-hole 6" x no-hole 6" x 6-hole Backup Pad for Roll Lock "Quick Change" Discs Specifications Diameter Size 1-1/2”, 2”, 3”, 4” Hub Type Type 1 Push-on Hub Type 2- SCREW-on Hub (Type S) Type 3- ROLL-on Hub (Type R) Reducer Bushing for Unmounted Flap Wheel REDUCE ARBOR SIZE From To size 1" 5/8" 1" 1/2" 1" 3/4" 1" 7/8" 1-3/4" 1-1/4"