... 2. Straightness and hole quality 3. High penetration rate DTH drill hammer With yeas of experience, now Zhongrui can manufacturer the best ... quality DTH drill bit, DTH drill hammer and chisel bit, thread button bit. Now we can ... (3.5"-10") DTH drill bit, 340,350,360,380, COP44, COP54, COP64, COP84 , 3"-8" DTH hammer, 340,350,360,380 ...