... in China ISO9001:2000,SGS certification. Electroplated diamond core drill bit for mine, coal mine drill bits ... kinds of drill bit. the size is following:1, Double tube drill:Φ28,Φ36,Φ46,Φ59,Φ60 ... 1, soft layer: Alluvial soil layer;Mud ash zone;sandstone;shale;2,middle-hard stone:Fine single limestone;Reinforced concrete ... and diamond segments. cutting bits,core drills. super quality mineral core drilling