CIR90 Low Air Pressure DTH Drilling Tools for Construction DTH bit is our main product. After many years searched, we have rich experience in development and manufacturing high quality products, which adopted high-quality raw materials, advanced technology and passed through strictly inspection. 1.high and low air pressure down-the-hole drill bits 2.Low air pressure hole Dia.:65-220mm 3.Face type: drop center / concave / convex / double gauge / flat