... medium-to-medium hard formations.3)The HSN rubber O-ring provides adequate sealing for bearing durability. Metal-face ... Size: 6",6 1/2",7 1/2",8 1/2",9 1/2",9 5/8",9 7/8",12 1/4",17 1/2", etc. IADC Code ... and seizure resistance of the bearing are improved. 2.Premium O-ring, Optimal seal compression and curved seal structure ... AvailableSize: 5 7/8",6",6 1/2",7 1/2",7 7/8",8 1/2",9 1/2",9 5/8",9 7/8 ...