... . 5.Current Main Availability Diameter/InchIADC CODE3 1/2 211, 121, 241, 537….3 7/ ... 1/2 211, 121, 241, 537….14 3/4 131, 211, 537, 517….15 1/2 211, 121, 241, 537….17 1/2 ... 131, 211, 537, 517….18 1/2 211, 121, 241 ... , 537….………..………………………………26 131, 211, 537, 517…. API standard 17.5'' sealed steel tooth tricone bit ...