Drilling tools manufacturer / supplier in China, offering 6 3/4 Inch IADC 517 537 617 637 Tricone Roller Bit, 6 3/4 Inch IADC 517 537 617 637 Roller Cone Bit, 7 7/8 Inch IADC 517 537 617 637 Tricone Roller Cone Bit and so on.