Overburden Casing System, Button Bits, Shank Adapters manufacturer / supplier in China, offering Versatile 114 140 168 219 Symmetric Casing System: Pilot Bit and Ring Bit Included, Heavy-Duty Ring Bit for Casing Tube Od 114mm, Compatible with DHD3.5 Hammer, DTH Drill Bit for DHD112 Hammer and so on.