China 8 1/2" IADC Code 637 Single Roller Cutter with Full Insert Roller Cones Bit Replaceable Bit Rock Drillng Bit, Find details about China Single Roller Bit, Roller Bit from 8 1/2" IADC Code 637 Single Roller Cutter with Full Insert Roller Cones Bit Replaceable Bit Rock Drillng Bit