... drilling rate and added cutting structure durability in medium-to-medium hard formations .The HSN rubber O-ring ... or oil well drilling2,Model: various kinds and according to the requirements of customers3,Material: ally steel, tungsten ... li mestones. Size and IADC available: 3 3/4" to 26" IADC 415,435,445,417,437,517,537 ... 1(12 1/4”),346.0 (13 5/8”),349.2(13 3/4”)374.6(14 3/4”)381(15”),393.7(15 1/2”),406.4 ...