... in medium-to-medium hard formations.3)The HSN rubber O-ring provides adequate sealing for bearing durability. Metal-face sealed ... and seizure resistance of the bearing are improved. 2.Premium O-ring, Optimal seal compression and curved seal structure can enhance ... 2",7 1/2",7 7/8",8 1/2",9 1/2",9 5/8",9 7/8",12 1/4",14 3 ... to minimum.Main Type AvailableSize: 8 1/2",9 1/2",9 5/8",9 7/8",10 5/8",12 1/4", etc ...