... of large torque, wide drilling range and durable 2.underground coal mining 3.long service lif geological drill bitThe bit can be ... used together with various drill machine in underground coal mining.The base body is machined by advanced numerical control lathe ... can be used together with various drill machine in underground coal mining.borehole dia.: 55, 65, 75, 80, 85, 94, 113, 133 ...