... 1/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series, 6-- Series,etc. Elastomer sealed bearing TCI BitCutting StructureThe durability of premium ... 3/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series, 6-- Series,etc. Air Cooling Roller Bearing TCI BitCutting Structure The durability ... ",15",15 1/2",17 1/2", etc. IADC Code:5-- Series,6-- Series 8 1/2" Brawny IADC 517 TCI Tricone Bits