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