China Single Roller Bit 8 1/2" IADC Code 637 with Straight Shank Roller Cones Bit Full Insert Replaceable Drill Bit, Find details about China Single Roller Bit, Roller Bit from Single Roller Bit 8 1/2" IADC Code 637 with Straight Shank Roller Cones Bit Full Insert Replaceable Drill Bit