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