... inserts and hardfacing on the shirttail increases gauge holding capability. 3. Bearing Structure Air cooling roller bearing package. Balls lock ... Diameter/InchIADC CODE3 1/2 211, 121, 241, 537….3 7/8 131, 211, 537, 517….4 1/2 ... 211, 121, 241, 537….4 3/4 131, 211, 537, 517….5 1/2 131, 211 ... 241, 537….……….. ………………………………12 1/2 211, 121, 241, 537….14 3/4 131, 211, 537, 517….15 1/2 211, 121 ...