IVY Classic 42381 4-1/2-Inch Turbo Backing Pad with 5/8-Inch - 11 Thread Locking Nut, 1/Card For using 4-1/2-inch resin fiber discs on 4-1/2-inch angle grinders with 5/8-inch - 11 threaded spindles, Flex-Abrasive (Registered Trademark) Raised spiral ribs and vents form air-flow channels which cool the discs and extend operating life Metal reinforcing ring is connected to backing pad with three pins to strengthen construction Includes 5/8-inch - 11 Locking Nut Pad Diameter: 4-1/2-inch, Locking Nut Arbor: 5/8-inch - 11, Max RPM: 13200