... medium-to-medium hard formations.3)The HSN rubber O-ring provides adequate sealing for bearing durability. Metal-face sealed bearing ... Type Available Size: 6",6 1/2",7 1/2",8 1/2",9 1/2",9 5/8",9 7/8",12 ... resistance and seizure resistance of the bearing are improved. 2.Premium O-ring, Optimal seal compression and curved seal structure can enhance ... 8",4 3/4",6",6 1/2",7 1/2",8 1/2",9 1/2",9 5/8",9 7/8", ...