... , now Zhongrui can manufacturer the best quality DTH rock drill bits, DTH hammer and chisel bit, thread button bit. Now we ... can supply 90mm-254mm(3.5"-10") DTH rock drill bits, 340,350,360,380, COP44, COP54, COP64, COP84 , 3"-8 ... -A 6-1826Q9-1826QConcave face, Concentric Casing System With Ring Bits ZRTG140Outer dia.of casing tubeInner dia.of casing tubeOuter dia ...