... The HSN rubber O-ring provides adequate sealing for bearing durability.637Hard Formation TCI Tricone BitsThe 637 ... formations. The HSN rubber O-ring provides adequate sealing for bearing durability. SizeBit TypeIn.mm6152.4517G, 537G, 617G ... , 637G9 1/2241.3437G, 517G, 537G, 547G, 617G9 5/8244.5437G, 517G, 537G, 547G, 617G9 7/8250.8437G ... 637G17 1/2444.5517G, 537G, 617G, 627G, 637G 5 7/8"TCI Tricone Bit