... /2",9 5/8",9 7/8",12 1/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series ... /8",9 7/8",12 1/4",14 3/4",17 1/2", etc. IADC Code:4-- Series, 5-- Series ... 3/410 5/8,12 1/413 3/4, 17 1/2,22, 24,26417 427 437517 527 537617 ... 3/410 5/8,12 1/413 3/4, 17 1/2,22, 24,26M223,M322,M316,M222,M416, ... The higher the series number the harder more abrasive the rock formation is. 2nd number is the relative degree of hardness ...