The 4 aluminum backer is 5/8-11 Thread. 106 Pieces of 4 Diamond Polishing Pad for granite marble concrete. 4 Pieces of 4 Professional Grade Glaze Buffing Pad (it brings granite marble stone mirror like polished result). 4 Pieces of (5/8″-11 Thread) 4″ Aluminum Backer/Pad Holder. Remind: Aluminum Backer’s max velocity is 5000 RPM. Please do not use it with high speed grinder / polisher. 106 Pieces 4 Diamond Polishing Pad for granite marble concrete. 20 X Grit 50 100 200 400. 8 X Grit 800 1500. 5 X Grit 3000 10000. 3.2mm thickness. Recommend 2500 – 5000 rpm (grinder speed must be lower than 5000 RPM). Wet or dry use (wet use recommended).