... ",9 7/8",12 1/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series, 6-- Series,etc. 2. Elastomer sealed ... ",12 1/4",14 3/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series, 6-- Series,etc. 3. Air Cooling ... ",9 7/8",10 5/8",12 1/4", etc. IADC Code:5-- Series,6-- Series,7-- 4,Non-Sealed Roller Bearing ... 1/4",15",15 1/2",17 1/2", etc. IADC Code:5-- Series,6-- Series IADC 517 537 8 1/2" tricone bit